Consider the following scenario:
You use Microsoft Lync 2010 and Microsoft Outlook on a computer that is running Windows Vista.
The tracing feature is turned off in Lync 2010.
You exit Outlook.
In this scenario, Windows Task Manager shows that the Outlook.exe process is still running. Additionally, you cannot start Outlook again unless you end the Outlook.exe process.
To resolve this issue, install the following cumulative update:
2496325 Description of the cumulative update package for Lync 2010: April 2011
To work around this issue, turn on the tracing feature in Lync 2010 by using the following Lync Server Management Shell cmdlet:
Set-CsClientPolicy -Identity client_policy_name -EnableTracing $true
Note The client_policy_name placeholder signifies “Global” unless the corresponding Lync 2010 client has a customized policy that uses a different name.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.