I did a more drastic version of this and it seems to have worked.
https://discussions.apple.com/thread/1570767?answerId=7434287022#7434287022
Library is now hidden in finder, so you have to use the "GO" menu > Connect to Folder
and type /Users/YOURNAME/Library/ into the box.
***
Navigate to this location in the Finder:
Macintosh HD/users/YOURUSERNAME/Library/Preferences
And delete the following files:
com.apple.ichat.AIM.plist
com.apple.ichat.plist
com.apple.ichat.subnet.plist
com.apple.ichatAgent.plist
***
I did an extra step - I went to Caches (in the main Library folder) and deleted the folder com.apple.iChat
Reboot. And it worked.
Before you empty trash make a copy of everything you're about to delete in case it entirely breaks.
I can't guarantee it will work, but it's fixed all of my iChat issues here, and I figured I had nothing to lose anyways.