If you see any of the below errors in your Lync 2010 Front End servers event log, changes are you may have used capitalisation in the “SIP:” notation pre-pended to the SIP address.
e.g. SIP: firstname.lastname@example.org
The Lync control panel will tell you when you forget to add “sip:” but fails to inform you the “SIP:” will cause issue.
A valid URI was not specified for the queue time out destination.
The Match Making service could not transfer the call because of an error in the queue configuration.
The workflow runtime encountered a critical error.