You receive this error message if the following conditions are true:
- The assembly that is specified in the error message is a signed assembly and is not installed in the Global Assembly Cache (GAC); instead, the assembly is in the Bin directory of the ASP.NET Web application. -and-
- Your ASP.NET Web application has just been restarted.
For more details refer PRB: ‘Can not Access File ’AssemblyName’ Because It Is Being Used by Another Process’ Error Message in ASP.NET