trashing prefs is probably not the way to proceed
there are lots of issues with sending to STP multitrack - a lot of them will go away if you send without video.
select the sequence, then choose send to STPMT from the menu, then in the dialogue that follows choose not to include video.
if that works then you can export a QT from FCP and add it to the STP project afterwards
in fact i'd recommend this as a preferred workflow anyway but that's cos i don't like ref movies.
if you still get an error without the video scan your timeline for any 'weird' clips - if there's anything a bit suspicious you can select it as a single clip, in the timeline, right click on it and send it to the multitrack to see if that's the offending article. you will get the same error message if it is.
hope that helps!!!!