I am running accessible Joomla 1.0.11. When I log in, the login module (which says Hi, [NAME] and displays a logout button) also displays an "undefined variable at line 61" error.

It's a simple problem and a simple fix. The code checks if $_VERSION->PRODUCT is "Mambo" or "Joomla!", and then defines $version. My $_VERSION->PRODUCT though, is "Accessible Joomla!". I added a check for that with the joomla test:
[code:1]elseif($_VERSION->PRODUCT == "Joomla!" || $_VERSION->PRODUCT == "Accessible Joomla!"«»){[/code:1]

Just thought you should be aware of this potential "3rd" version in case a similar check is happening elsewhere.

Glad to help!