I have tried to export my work on CT6 many times ind different formats DV Pal and wmv, but viewing the playback it does not pick up speed, it runs for a few seconds, and then stops, and the sound and picture is not in synk during playback - Can anyone help, please?

I am working on a new imac with windows 7 x64 Vitual Machine - I have not had any other problmes using CT6 Pro and dont have problems using any other programs.