as black_pearl_27 said, it is still a codec problem.
where's Jaddziadax when you need her...
I'll just post a pic she put up. (it probably took longer to find it than it would have taken for me to make and upload one myself...)
see the two circled buttons? those are the mark-in and mark-out buttons.
go to the first frame that you want to encode and click the mark-in button (the one on the left)
go to the last frame you want to encode and click the mark-out button (the one on the left)
if your selection is big enough, you will see that blue bar.
it marks the footage that will be encoded when you save
by default, vdub/mod selects all of the video that you import.
now go to file and click "save as"
near the bottom, you should see a box that says "full processing mode"
you can change it to fast recompress...but it won't really hurt your video quality if you leave it as full processing mode.
below that should be the codec that your video will be encoded with. If it doesn't say huffyuv or lagarith, click the "change" button and select huffy or lagarith from the list.
(you can also do this by going to video and clicking "compression". it'l give you the same list of codecs, the only difference is where and when you select the codec)
after that, name your file and click save.
if you are still unsure about vdubmod, read this