avi-targa?
Not sure I understand, is it an avi or targa sequence.
it sounds like an issue with the alpha channels, I don’t think avi clips can carry alpha only rgb.
If its a targa seq check the sequential file setting, ie. is it pulling in the right duration of sequence, even if it is a white field!
Check your avid import settings, ignore alpha if its a full frame sequence, try invert alpha? Do you have ae? Or if its a file seq you can batch precess it in photoshop, ie. open-save as etc etc