Can you run the 1.4 code you downloaded (in debug mode) against your live database (or better still, a local copy of that database), and debug locally in that way?
I'm curious if the desktoplayout is causing any of the errors, since you said you 'got it to work'. Was it causing problems before? Can you use a different layout without error?
Maybe I could see something in your error logs (it sounds like you hae plenty of them). Can you send me one of the more average-sized ones?
It might be easier overall to migrate the database to 1.6 code. I think that's the stable release version...