Why do I get the error message ‘Access is denied : <myctrl>’ when I try to load a Custom Control

This is a common problem in ASP.NET. It happens because some program is scanning the Temporary ASP.NET files folders where your assemblies are copied. They have the files open in a mode that prevents ASP.NET itself from using the assembly file.

For solution refer PRB: Access Denied Error When You Make Code Modifications with Index Services Running