if(pluginDescriptor.OriginalAssemblyFile.Directory.Exists)
CommonHelper.DeleteDirectory(pluginDescriptor.OriginalAssemblyFile.DirectoryName);
instead of this
if(pluginDescriptor.OriginalAssemblyFile.Directory.Exists)
CommonHelper.DeleteDirectory(pluginDescriptor.OriginalAssemblyFile.FullName);
according to https://msdn.microsoft.com/en-us/library/c1sez4sc(v=vs.110).aspx
since the current code gives this error "The specified path is invalid"
It is in pluginmanager.cs line 821