Not able to catch "Access Denied" exception

[Sachin Arey]

Hi,

We have developed ASP.NET web service for Windows sharePoint services
and web service client. This web service calls SharePoint object
methods
internally.
For exceptions, we have put try/catch blocks. From SP OM calls, we get
exception with message "Access Denied".
Even if we catch this exception in the web service, it is carried over
to web service client on executing code within catch block.
On catching exception on client side, we get message "The
request failed with HTTP status 401: Unauthorized".

Is there any way we can catch exception with "Access Denied" on server
itself properly? I use following exception class.
try
{
}
catch( Exception exe)
{
}

Is there any special exception class for catching such "access denied"
failure?

I really appreciate help in this regard.

Thanks and Regards,
Sachin.