Okay, so I have a WRT54GL running DD-WRT. Many people have those. The problem, however, started when I moved my desktop PC from wireful to wireless. For some reason, My laptop (also wireless) could not reliably access windows file shares. It would access some of the folders some of the time, and most of the folders none of the time.
I toiled and troubled over it to find out what was wrong, but nothing. Windows was running fine, of course, since when I connected one of the two PCs wirefully they were fine, but when both were on wireless they couldn’t access each other’s file shares. They could access the wired server fine, however, and pings/tcp/everything else worked well between them. Just no file shares.
The problem turned out to be IPX, and more specifically NetBIOS over IPX. I don’t know what exactly caused it, so I’ll say it’s the router. A simple fix for it was to remove the IPX protocol from the list of installed protocols so that you force Windows to use NetBIOS over TCP. No big loss, I think. Time will tell.