IsolatedStorage with impersonation in ASP.NET problem

[Zdenek Drlik]

Hi,
I have an ASP.NET application. I want to use IsolatedStorage in this
application. When I run this application with anonymous access set in
IIS (user set to IUSR_<machine>) and impersonation set to false in
web.config, IsolatedStorage works fine.
But when I try to set impersonation to true via the web.config, calling

IsolatedStorageFile.GetUserStoreForDomain()

get me an IsolatedStorageException with this call stack:

System.IO.IsolatedStorage.IsolatedStorageFile.nGetRootDir(IsolatedStorageScope
scope) +0
System.IO.IsolatedStorage.IsolatedStorageFile.InitGlobalsNonRoaming(IsolatedStorageScope
scope) +42
System.IO.IsolatedStorage.IsolatedStorageFile.GetRootDir(IsolatedStorageScope
scope) +98
System.IO.IsolatedStorage.IsolatedStorageFile.GetGlobalFileIOPerm(IsolatedStorageScope
scope) +208
System.IO.IsolatedStorage.IsolatedStorageFile.Init(IsolatedStorageScope
scope) +37
System.IO.IsolatedStorage.IsolatedStorageFile.GetStore(IsolatedStorageScope
scope, Type domainEvidenceType, Type assemblyEvidenceType) +66

System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForDomain() +12

and tells me that storage directory cannot be created (System could not
find specified file).

Does anybody know what's wrong, or how to use IsolatedStorage with
impersonation in ASP.NET?
Thanks

Zdenek Drlik