In past release of Lync/Communicator, we were trying to release memory using 

System.Runtime.InteropServices.Marshal.ReleaseComObjectLyncClient.GetClient());

With Lync 2013, I get the following exception

{"The object's type must be __ComObject or derived from __ComObject.\r\nParameter name: o"}

How can I tell the Lync API to free up memory when I am done with it.

You might want to ask your question on MSDN forums for Lync development: http://social.msdn.microsoft.com/Forums/en-US/home?category=uc