After pressing enter key - there is a msg in Windows 7

Question

Hi All,

The program is in c# windows apps on Visual Studio 2003.
In program if user press enter key  then tab key is send internally...It is working fine for all this year's.

But now in Windows 7 it is giving below error msg :

The application attempted to perform an
operation not allowed by the security plocy.The
operation required the SecurityException.To
grant this application the required permission
please contact your system administrator,or use
the Microsoft.NET security policy administration tool.
Click Continue and application wil ignore this error and
attempt to continue.
Unable to create Hook.
<Detail>                              <Continue>

I have tried runnin the shortcut in compatiable mode & run as administrator.
Installed .Net 1.1 Service pack ....But still same problem.

Regards

Shehzad