The IServer::GetLastError method returns an ASP error object that describes the last error that occurred while running a script.
HRESULT GetLastError( IASPError *ppASPErrorObject // pointer to an IASPError
);
If a custom error has been defined for a virtual web server, ASP application, directory, or file, it may refer to an .asp file. If this is the case, when an error occurs during the running of an .asp file the server will automatically transfer to this asp file via the IServer::Transfer method. All of the state information from the executing .asp file will be available to the .asp file that is handling the error. In addition, the methods exposed by the IASPError interface will be available.