I have had a few reports of this error being raised and the interface being unresponsive:

" NSReceiverEvaluationScriptError: 4 (1) "

This turned out to be caused by the MegaZoomer and NuclearMouse SIMBL plugins. After disabling them SyncTunes behaved as it should.

There may be more plugins that cause problems, so let me know and I'll maintain a list.