XMLSerialization: Sometimes csc.exe freezes on the PermissionSet

[A programmer desperatly needing help!]

I use the xmlserialization on asp.net pages and on previous machines it never
gave a problem.
But now i somethings get a:
Timed out waiting for a program to execute. The command being executed was
"c:\winnt\microsoft.net\framework\v1.1.4322\csc.ex e" /noconfig
@"C:\DOCUME~1\...\ve3y0f-a.cmdline"

error. It happens at random but occurs mostly when calling the
XMLserialization multiple time rapidly.
While looking at the .out file the error displayed is:
error CS0647: Error emitting
'System.Security.Permissions.PermissionSetAttribut e' attribute --
'Unspecified error '

It occures at the this line in the .cs file:

[System.Security.Permissions.PermissionSet(System.S ecurity.Permissions.SecurityAction.LinkDemand, Name="FullTrust")]

The csc.exe process hangs and stays in the task manager and the files he
created (.out, .err, .cs, .cmdline and a 0Kb dll) stay in the ASPNET temp
directory until i kill the process. The webapplication hangs also.

Could anybody give me a clue of what causes this problem and how to fix it.
I think it has something to do with getting the permissions.

Thank in advance.