An error occurred while accessing IsolatedStorage.

While developing a Silverlight Windows Phone 7 app I ran into this problem: when the application closes, an internal  IsolatedStorageException is raised:

An error occurred while accessing IsolatedStorage.
   at System.IO.IsolatedStorage.IsolatedStorageSecurityState.EnsureState()
   at System.IO.IsolatedStorage.IsolatedStorageFile.get_AvailableFreeSpace()
   at System.IO.IsolatedStorage.IsolatedStorageSettings.Save()
   at System.IO.IsolatedStorage.IsolatedStorageSettings.TrySave()
   at System.IO.IsolatedStorage.IsolatedStorageSettings.SaveAllSettings()
   at MS.Internal.FrameworkCallbacks.ShutdownAllPeers()

IsolatedStorageSettings seemed to be the cause of the problem. Very weird because I wasn’t even using it! Just adding this line in my App class would cause the problem:

private System.IO.IsolatedStorage.IsolatedStorageSettings appSettings = System.IO.IsolatedStorage.IsolatedStorageSettings.ApplicationSettings;

Now I created a new, empty, project (Windows Phone Application) and inserted that line. Weird: no problems.
I thought there was something wrong in my solution, so I made a backup copy and started removing stuff. At some point my solution was identical to the default one (except for the IsolatedStorageSettings line and the project’s GUID). Not “almost identical”, but completely, literally identical, i.e. WinMerge found no difference except the two mentioned. And of course the default solution worked while mine gave the IsolatedStorageException on shutdown.

I honestly haven’t understood the cause of the problem, but at least I’ve found a solution: change the project GUID:

  • close Visual Studio
  • open your solution’s .sln file with notepad
  • replace a couple of numbers in the Project(“{<your GUID here>}”)
  • open the .csproj with notepad
  • apply the same change to the GUID (in the first line after the comment and in all the Build Configurations)
  • Re-open your solution with Visual Studio and the problem is gone.

I suspect the problem has something to do with the emulator but I haven’t had a chance to try a real device yet. I hope I saved you an evening of head scratching.

Windows Phone 7 Marketplace subscription for Swiss individuals

Lately I’ve been busy coding stuff for Windows Phone 7 –really fun! If you are a Swiss individual (i.e. you are not developing your apps for a company) then joining the Marketplace is not very straightforward. If you reside in another non-U.S. country you may as well read this post, I suppose you will only have to make minor changes to the procedure.

Sascha Corti of Microsoft Switzerland has provided a great walkthrough, but I whish to add a couple of things, in particular re. obtaining your notarized passport copy.

Sign up

First, you can sign-up to the App Hub on You need a credit card to pay the CHF 129 annual fee. Be careful: the publisher name is final and cannot be changed later. So think about it for a minute and if you are not sure wait until you’ve decided what to display as your apps’ publisher.

Payee Details

When you are signed-up and have clicked on all the confirmation links you receive, you have to log into your account and fill in your bank account data under my account/payee details. If you only have a Post account, no problem, use the Post’s IBAN calculator –they also provide the BIC and correct address.

At this point you are ready to submit your applications to the marketplace, but you may want to continue reading. In fact as you probably already know, you will receive 70% of your app’s total sales, the other 30% being kept by Microsoft. The problem is that as a non-U.S. resident, another 30% will be removed from your part –which is a rather big hit IMO! Keep in mind that you will have to pay Swiss taxes on the income, so in the end not much will be left in your hands.

That’s why you have to provide some documentation proving that you are indeed paying taxes on your country –so that the U.S. won’t charge you that infamous additional 30%. In practice, it means asking an ITIN number to the U.S. International Revenue Service and giving it to Microsoft.

Notarized Copy

To ask an ITIN number you need a certified true copy of your passport. The IRS is rather strict on this aspect and won’t accept notarized copies from entities not in their list. This excludes the Swiss Post and probably anything else except the U.S. Embassy.

So -unless you live in Bern or Zurich and can take an appointment- you will have to send the following:

  • your passport
  • a copy of your passport
  • the filled-in W7 form (more on that later)
  • the Microsoft printed letter (more on that later)
  • a CHF 1.00 stamped envelope with your address

to this address:

U.S. Embassy
Consular Section
P.O. Box
3001 Bern

and at the same time, pay CHF 50.- (plus the 18.- postal fee) to

American Consular Services
Sulgeneckstrasse 19
3007 Bern

Yiikes! This will probably be the most expensive photocopy of your life (also considering that you made the copy itself :-) ), but they don’t have a post/bank account so you cannot avoid the 18.- fee.

W7 Form

In some days you will receive your notarized passport copy (and hopefully your passport) back. You are now ready to forward the W7 form. If you sent it to the embassy, they will probably have checked it for obvious mistakes, but I have not yet received mine back so I cannot tell at this time.

Anyways the W7 form can be downloaded here. Fill it in as explained in Sascha Corti’s presentation. In particular make sure that you check point a. and h., and enter “Exception 1 (d) – Royalty Income”  at point h., plus “12” as treaty article number.

Now log into your Marketplace account, go to the payee details page, scroll down until you find “Click here to download the Microsoft letter”, download the letter, print it and hand-write the date and your full name. Make sure the letter includes Todd Biggs signature at the end. A previous version did not include the signature and applications were rejected because of it.

Now send W7 and the letter to

International Revenue Service
ITIN Operations
P.O. Box 149342
Austin, TX 78714-9342
United States of America

After n weeks they will hopefully assign you an ITIN number.

W-8BEN form

With your ITIN in hand, you can finally fill in the W-8BEN form, print it, sign it and send it to

’Windows Marketplace for Mobile’
One Microsoft Way
Redmond WA 98052
United States of America

Once they receive and process it you should be free of the 30% tax and receive your full 70% royalties. As far as I understand it this is not retro-active, i.e. the taxes you previously paid won’t be reimbursed.

That’s all

This should be all (I never said it was simple ;-) ). It takes some effort, time and money (about CHF 80.- one-time plus the annual 129.- fee), but if you are doing some interesting apps it may be worth it as you will hopefully earn it back soon.


Getting your ITIN number from the IRS can take a long time. It took me more than 3 months since I sent the W7 form. Send it with signed mail for piece of mind, and be patient, they will eventually answer.

Best of Swiss Silverlight 2010

During this year’s Shape 2010 conference in Zurich-Oerlikon, Microsoft Switzerland announced the winners of the Best of Swiss Silverlight 2010 Award in collaboration with the Best of Swiss Web Association, simsa and Netzwoche.


Incredibly my application Trails of Switzerland won the Bronze award. I was completely taken by surprise (not to mention super excited) because I didn’t really expect anything when I started the project. In fact it was just a “weekend project” to try a couple of things. When I saw the award application form I thought it could be worth a try so I polished a bit the front-end and added a couple of cool gadgets.

I was familiar with the competition’s application procedure also because I already did it a few times before for my company (that won this year’s .NET Award by the way).


My application leverages Silverlight’s DeepZoom component to show a full topographic map of Switzerland. The base image is a huge 19 Gigapixels (~3 Gigabytes) JPEG, but movement and zooming is wonderfully smooth.

The tricky part was mapping the GPS data to the map and then keeping content synchronized with the DeepZoom zooming and panning.


Currently Trails of Switzerland is in closed-beta at and will probably never go live (except if someone wants to buy it from me) for the simple reason that copyrights on the maps are incredibly expensive and I cannot afford to buy them “just for fun”.
To be honest I must say that the Swisstopo maps are of incredible precision and quality, but still are way too expensive for a no-profit application.

The good part is that Trails of Switzerland could probably be ported to Windows Phone 7 (with a major restyling of course) as DeepZoom seems to work very smoothly there too.

I’d like to congratulate the other contest winners (Coresystems AG/Misapor, Extrafilm AG, VASP Datatecture AG/ETHZ, Portia AG/Immostreet AG): your applications were really mind-blowing!


The conference was very interesting as well. In particular Bob Muglia should have taken notes from Ronnie’s talk on HTML5/Silverlight. If you have watched the PDC2010 keynote (and the twitter/blog-storm that followed) you know what I’m talking about.

As always Laurent’s Bugnion’s talks were interesting, but also many others were worth the trip (in particular from a Windows Phone 7 and design/UX standpoint).

Moral: you never can tell

Moral of the story is you never know where a weekend project is going to bring you. It seems that someone else also agrees on this. This is one of the things I love in this field.


Thanks to Microsoft Switzerland and most of all thanks to my wife for the continuous support and for understanding when I forget stuff/don’t listen because I’m thinking about code (i.e. most of the time) :-)