Hi,
With iChat Open go to the iChat Menu > Preferences > Alerts pane.
In here select the top drop down to read "Message Received"
Is this set to run an AppleScript item ?
Is it the one that Reformats Text ? (Mix Message Case)
This little script is added to Hard Drive/Library/Scripts/iChat for iChat 5 in Snow Leopard.
Mostly, it seems, it was expected to be used for outgoing IMs but the Selection process in the Alerts pane means it can reformat incoming ones as well.
9:52 PM Saturday; January 29, 2011
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"