Many of the uploads from my shared folder are listed as "File not found" in the uploads monitor window. I checked my shared folder, and the files are there and with the proper extensions. I've refreshed the library a few times but I still get this error message. Is this happening because I might have too many files (700+) in my shared folder? Not too worried, just curious.

Macintosh G4 933/OS 10.1.5.1/1gb memory/Cable Modem

That happens if you are refreshing your library. Every file has a certain position in your library, to identify it, in case you are sharing files with the same name. Some client received a response from you containing the file at its old position and is now trying to download it.

The problem is that some servents (Gnucleus, Bearshare) will try again and again, although they receive a 404 everytime they download. Eventually they will stop, but it can take them a couple of minutes.