I did all that but there was no problem playing back, previewing or re-exporting ogg theora files.Obviously, something must be wrong at your end. Nevertheless, let me know if I can do anything to help.tell me if this happens for you too.
import mp4, put it in a track, export to ogg theora. fine no problem.
then import the ogg theora to a new workspace put it in a track then export it to ogg theora or even just preview it. does it produce a multicolored pixilated screen that changes i.e, not your original video images at all.
Cheers.