I recently changed the name of the main user on my Mac and since then I have been unable to login to Lync.
I have uninstalled Lync (properly, by deleting all folders in library) then reinstalled Lync and I also repaired the permissions in the disk utility. To make sure this was an issue with my user folder, I created a new temporary user and installed Lync under the account for the temporary user and experienced no issues when opening the application.
I have a copy of the error message I receive when opening Lync under my main user account, but it is quite long. I can post it if necessary.