Consider the following scenario: You access an invalid conference URL in a Microsoft Lync Server 2010 environment. Then, you receive the following error message:
Error: Meeting URL is not valid.
This issue occurs because Lync Server 2010 does not change the language of the strings in the default Web page resource file.
To resolve this issue, install the following cumulative update:
2571547 Description of the update package for Lync Server 2010, Web Components Server: July 2011
Here is the KB link.