Adium just auto-updated to the latest version (1.5) and upon restart I was alerted that my SIPE Plugin was not supported on this architecture. Bummer.
I’m not sure, but it looks like I was running a 32bit version of Adium and the update pushed me into 64bit territory. I’m totally fine with that, but the SIPE plugin was 32bit.
This morning I found this ticket in which some intrepid individual posts a complied 64bit version for our enjoyment.
Download the “SIPEAdiumPlugin.AdiumLibpurplePlugin(64bit).zip” file linked to above. Uninstall the old via the Adium Xtras Manager (From the Adium menu) and double-click the new plugin contained in the aforementioned .zip file. Voila, back to chatting on the corporate Microsoft Communicator/Lync network.
Update: Edited language to be more clear.
Update 2: This plugin will install in Adium 1.5.1, but will not work without running this command in the Terminal.
Update 3: I just updated to 1.5.2 this afternoon (July, 24, 2012). It appears this update undoes the work in update #2. If you view the Accounts tab in Adium Preferences you’ll see your SIPE account hang at ‘Connecting’. Close Adium and run the commands linked in update #2 to get thing working again.