Smuxi's Twitter support is currently not working as Twitter has changed the API and revoked Smuxi's API keys. Twitter now expects an open-source app to pay monthly for API access.
@jeremyp3@meebey Can you paste bin the output of the error message? You can capture the error output into a file by staring Smuxi from a terminal like this: smuxi-frontend-gnome > smuxi-crash.log