Hi Craig,
To use Lync for Mac 2011, we need to take some additional steps.
First, please install this update for Lync for Mac 2011: www.microsoft.com/.../details.aspx
After that, provide the following information in Lync for Mac client:
1. In the Microsoft Lync for Mac sign-in window, type your Office 365 email address, user ID, and password. Use the same user ID and password that you use to sign in to Office 365, for example, aprilr@contoso.onmicrosoft.com.
2. Click Advanced.
3. Under Authentication, clear the Use Kerberos check box.
4. Under Connection Settings, click Manual configuration.
5. In both the Internal Server Name box and the External Server Name box, type or paste sipdir.online.lync.com:443.
6. Click OK.
7. In the Microsoft Lync for Mac sign-in window, click Sign In.
If this issue persists after doing the above steps, please feel free to post back to do some further troubleshooting.
Thanks,
Young Yang