If you are sure that the recorded games are in the right folder, there could be 2 problems :
- the files that you've downloaded are corrupted
- AOM got a bug and can't read records anymore.
First, to check if your file is corrupted or not, you will need a software called hashcalc : http://www.slavasoft.com/zip/hashcalc.zip
When you download a record, for example this one, on the web page, clic on "Show more" and note the "md5 checksum".
Then download the file on your hard-disk.
Launch hashcalc and open (with it) the recorded game you've downloaded, then calculate the md5 checksum and compare with the md5 checksum given by the website.
If both checksums are egal, you are sure that your file is not corrupted.
So, second possibility, that means your AOM can't read the recorded games anymore, and Hades has already given the solution : Reinstall AOM.
Hope you'll fix it soon.
The best defence is attack!