Consider the following scenario:
You deploy a custom application in the Microsoft Lync Server 2010 environment. You do this by installing a Microsoft SIP Processing Language (MSPL) script on the Lync Server 2010 front-end server. The MSPL script uses the QueryCategory function to verify the user status.
A Lync 2010 user invites another Lync 2010 user for an instant messaging session.
You verify the corresponding log in Event Viewer.
In this scenario, the log displays a warning message that states that the QueryCategory function returns a NULL value instead of the presence information as a string.
To resolve this issue, install the following cumulative update:
2500442 Description of the update for Lync Server 2010: April 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.