Master page Error ? : Sharepoint

This is a discussion on Master page Error ? within the Sharepoint forums in Microsoft Tools category; Hi, I am developing Custom workflow using Asp.net Forms. In forms i need to put refernce to my site master page . i used like .. Spweb nsite = SPControl.GetContextWeb(Context); this.MasterPageFile = _nsite .MasterUrl; i am getting error like The virtual path '/_catalogs/masterpage/default.master' maps to another application, which is not allowed. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentException: The virtual path '/ _catalogs/masterpage/default.master' maps to another application, which is not allowed. any help ...