Still Problems with Thread Impersonation

Hi,
I already posted to this newsgroup, but didn't get an answer. So I try
again:

I've got an ASP.NET Web-Application written in C#.
In IIS 6.0 (Windows Server 2003) I have set the application to allow
anonymous access (using the default Account IUSR_<servernam e>). In
Web.config I have set
<identity impersonate="tr ue" userName=<myUse r> password=<myPWD >/>

Everything works fine exept for this:
In my application, I start a thread. I know that impersonation is not
taken over by the thread so I copy the current impersonation by

System.IntPtr windowsIdentity Token;
System.IntPtr newToken = System.IntPtr.Z ero;
WindowsIdentity currentIdentity = WindowsIdentity .GetCurrent();
DuplicateToken( currentIdentity .Token, 2, ref newToken);
this.windowsIde ntityToken = newToken;

and inside the thread I re-impersonate with:

WindowsImperson ationContext impersonatedUse r =
WindowsIdentity .Impersonate(th is.windowsIdent ityToken);

After that, access to files inside the thread is working, but two things
don't work:

- Sending Mails: I get this error:
System.Web.Http Exception: Could not create 'CDO.Message' object.
on Command:
System.Web.Mail .SmtpMail.Send( msg);

- I also use encryption inside the thread. Command
SymmetricAlgori thm symm = new TripleDESCrypto ServiceProvider ();
leads to Exception:
System.Security .Cryptography.C ryptographicExc eption: Cryptographic
service provider (CSP) could not be found for this algorithm.

- Other accesses of COM-Objects also don't work...

If I don't impersonate the thread by commenting out
//WindowsImperson ationContext impersonatedUse r =
WindowsIdentity .Impersonate(th is.windowsIdent ityToken);
both commands work, but the thread can't access some files I need.

does anyone have any idea?

Thanks,
matthias