Rundll32 crash in thumbnailing .MPG

[OldAmateur]

I'm running under Vista Home Premium (not my choice -- it came with the new computer). When Vista displays the contents of a folder in thumbnail mode, when the folder contains video files, the op system creates a thumbnail for each file containing a frame from the underlying video. Recently, whenever that process begins for a .mpg file, it stops with an error message referring to rundll32.exe. (If I can figure out how to include an image here, I'll show a screen grab of the error message.) When I click on "Close the program", the system goes on to create the thumbnail. Other video files, like .avi, get thumbnailed without error.

Big deal, you say; but it is a big deal if I'm working with a folder that has a lot of .mpg files: the error repeats with each file that needs a thumbnail, it steals focus from the window I'm trying to work in, and it just generally annoys me. Don't use thumbnail mode, you say. Right, I would prefer to use detail mode, but when I try that, Vista keeps switching back to thumbnail.

Because it happens only with .mpg files, I'm guessing that the system is trying to use an MPG2 codec that is defective or is not appropriate in order to decode the frame from the video. I suspect that when the first codec fails, the system uses another codec that works, and the thumbnail results. (I'm sure I have at least half a dozen MPG2 codecs installed, because I have tried out many video viewer apps.)

So, can anyone help me figure out how to identify and to fix or bypass the uncooperative codec?

Many thanks.