The message styles are stored in ~/Library/Application Support/Adium 2.0/Message Styles/ . Try removing Candybars.AdiumMessageStyle and installing a new copy. Adium should replace message styles when you install new ones with the same name, but it's worth a try.

Susan: Which version of Adium and OS X? Did you try downloading it again? Cause I think I fixed that... it was an issue with the version of the message style not being compatible with Adium 0.77.

61Tipo61: Good to hear that. :)

sdh: Check your e-mail.

Apparently, I had upgraded the message style to the new format that is only available in Adium 0.8, and since I was in a rush to fix the issue with 10.3.9 I forgot to try it in 0.77 before I uploaded. I've uploaded a new version of 1.1 that will work. Sorry for any inconvenience.

61Tipo61: Did you update to 1.1?

mathuaerknedam: I had positioned the background image within background-image. When I used background-position instead, it worked fine. So it was kind of a stupid mistake.