Solution!!! Cannot sign in to Lync: Microsoft Lync 2010 is not a version that can be used to sign in to the server.

My customer logged a call to report issue encountered while trying to sign in to Ms Lync 2010 client this morning;

Investigation shows that MS Lync version 4.0.7577.0 is out-of-date and should be upgraded

Microsoft Lync hotfix was applied and it was automatically upgraded to version 4.0.7577.4445.

My customer's issue is now resolved.

You can download the required hotfix for 64-bit via Microsoft Download Center and 32-bit via Microsoft Download Center