I try to write to Isolated Storage but get this exception. I wonder what I can be missing ?

An unhandled exception of type 'System.IO.IsolatedStorage.IsolatedStorageException' occurred in mscorlib.dll

Additional information: Unable to determine application identity of the caller.

using namespace System::IO::IsolatedStorage;

		IsolatedStorageFile^ abc = IsolatedStorageFile::GetUserStoreForApplication();

            String^ Testfile= "Test57.txt";

                 IsolatedStorageFileStream^ a1 = gcnew IsolatedStorageFileStream(Testfile, FileMode::Create, FileAccess::ReadWrite, abc );
                 StreamWriter^ WriteFile3 = gcnew StreamWriter(a1 );