Importing into Collections

I have captured a number of mpeg files using Sonic MyDvd
software. When I try to import them into Collections, I
get the following dialogue box:

The file C:\VCR Tapes\Tape 1 Jul66-Jun68.mpg cannot be
imported because the codec required to play the file is
not installed on your computer. If you have already tried
to download and install the codec, close and restart
Windows Movie Maker, and then try to import the file
again.

After repeated attempts closing and restarting WMM, I
still get the same result. What else can I do?