.AVIs appear to be MPEG-4s on Nero *help please*

Hi guys, I’m having one of those rip-your-hair-out-because-of-frustration problems with Nero.

I got the software when I bought my Sony Dual Layer DVD Writer. The application that burned my TV shows on DVD was NeroVision Express. So it worked perfectly for a while after I first got it. Every once in a while, when first adding my files to the “burn list” a message would come up saying:

Due to patent restrictions, MPEG-4 decoding is not available.
Thank you for using Nero. Upgrade online now and get the newest full version of Nero, the ultimate all-in-one digital media solution, at a special discount.

And my files would be added to the list and they burned perfectly.

I didn’t burn much for a while, but today I tried to make a DVD and Nero will not allow me to add my .avis to the “burn list”. When I try, the box comes up saying:

Please wait:
Adding video files to the project…
(and it has a bar that fills up after the file is added)

So, it tries to load it, and the bar fills up completely but then a new message comes up saying:

Unable to insert C:\Documents and Settings… (and so on) and “OK” is your only option.

Then, after selecting “OK” the first message I mentioned appears (the one about MPEGs). And I know that my files are .AVIs. I even tried to burn a file that I had successfully burned in the past. Nothing worked.

Does anyone have any experiance with the problem? Oh, and non of my .AVIs will play on Nero ShowTime. The same message about MPEGs comes up. I would appreciate any help anyone would offer.