A blank window might display when you start Microsoft Lync 2010.
To resolve this issue, install the following cumulative update:
2514982 Description of the cumulative update for Lync 2010: November 2011
For more information about the similar issue with Office Communicator R2, click the following article number to view the article in the Microsoft Knowledge Base:
983215 A blank window opens unexpectedly when you start Office Communicator 2007 R2