Mpeg2snittE or PVA instrumento

Hi I have been trying to burn 3 recorded episodes of 6 feet under onto 1 dvd. Usully I have used PVA instrumento followed by Mpeg2 snitt before authoring and burning. This has worked fine with single films . But mpeg2 snitt will only recognise the merged video file up to the end of the 1st episode of 6 feet under .The sound continues but the video file just stops. Does anyone have any idea why this is and can it be fixed? TIA Rob