Comment 4 for bug 392066

On the ground of your debugging information there should be an decoding problem. It happens when the hamster-applet is querying the already existing activities for the autocompletion feature of hamster during the startup.
There is data in your database which is not stored in the unicode format UTF-8 and the hamster program cannot handle this.

Take a look on the table 'activities' in your database file 'hamster.db' with the SQLite data browser (a GUI for SQLite). You can install it with 'sudo aptitude install sqlitebrowser'. Maybe you can solve your problem manually.