As
@
Adamsville
said it might be a bum codec. My uncle has the same problem being on OFW with avi's; says there are a lot that work but the odd one here n there don't.
You can always use programs like Handbrake (I think will convert to ps3 compatible), and DVDFab I know will convert a ps3 compatible format.
Other than re-downloading the avi from a different source/group, I think the only option is to re-encode with proper software.