if you are using the IsolatedStorage for application configuration storage, and when you get the IsolatedStorageException on the client, pls ensure the 'Enable application storage' on the 'Application Storage' tab of the Microsoft Silverlight Configuration is ticked.
This issue can be found from the MSDN(http://msdn.microsoft.com/en-us/library/system.io.isolatedstorage.isolatedstoragefile.increasequotato(v=vs.95).aspx)
| IsolatedStorageException | The isolated store has been removed. -or- Isolated storage is disabled. |