We have been working with an issue in Lync 2010 clients where users were not able to sync their outlook calander information. After checking so many parameters and testing we found that issue is with one Hotfix KB2533999 which was causing issue.
To resolve this issue we had to remove this hotfix and run without patch and it fixed the issue.
There is also a hotfix KB2540951 available which would address this issue. You can install this patch on top of any previous patch if you not willing to remove.