So Trillian has not worked for me on windows for the past month or so since I installed that 3.1 update. It basically crashed on launch and full reinstalls had no effect. I think I chose not to install the MSN client update and thats what broke it. After much searching I found that all that needs to be done is a manual plugin update.. Notes below from a thread on Cerulean's forums:
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Replace the same named file(s) in C:/ProgramFiles/Trillian/plugins while Trillian is NOT running: