Hey guys,
Thanks for the responses.
@Lee, actually there was original video and TC on the tape. All i wanted to do was to stripe new audio back to the tape without picture and new TC.
Turns out the problem was that the Black Magic Card was selecting 8 channels of audio instead of the two, so the Beta Deck was not putting the two channels of audio that I wanted back to tape. I have now set it to the Two channel option, and all is working great!!!
Maybe this might be of some use to someone else in the same predicament!