Building a plugin with Release configuration fails with the error:”Can not access .sdlplugin because it is being used by another process"

Building for Release fails with the error:

”The process can not access the file C:\\...\Plugins\Packages\Trados_Plugin.sdlplugin because it is being used by another process"

I’ve cleaned the solution and even the Packages folder in both

AppData->Roaming->SDL->…11

and 

AppData->Local->SDL->…11

I run the “Process Explorer” and it didn’t find any process that was using this file. Please advise.

Thanks!