Error in Custom security extension for SQL Reporting services

If Custom security extension developed with vs.net 2003 is deployed to a report server having sql 2005 reporting services installed will throw an exception:
System.TypeLoadException: Method 'CheckAccess' in type '' from assembly '' does not have an implementation.

Obvious reason is :
IAuthorizaitonExtension has one overridable method CheckAccess with following signature

bool CheckAccess(string userName, IntPtr userToken,
byte[] secDesc, ModelItemOperation requiredOperation);

ModelItemOperation enum is new in sql 2005 reporting services which was not in earlier sql 2000.


Cheers,