migration to new server ends up with -> Security Exception

Hello,
Since I transfered a .NET website to a new server I receive a security exception.
On the old server it works fine, but the new server seems to have some difficulties with it.
Not all .NET pages go wrong, I can't seem to find what's triggering the error.
The complete error is:
Description: The application attempted to perform an operation not allowed by the security policy.  To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.

Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
Since I am the administrator, I would like how ...