Could not load file or assembly DotNetOpenAuth.Core

Hello, I have deployed one web application

I have not used any "DotNetOpenAuth.Core" files

and getting this error even after deleting "DotNetOpenAuth.Core" assemblies

Error is-

Could not load file or assembly 'DotNetOpenAuth.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=2780ccd10d57b246' or one of its dependencies. The system cannot find the file specified.

thanks in advance