Personal File Sharing...Please Help!

Here's the problem that I hope someone can help with.

At home, I have an Airport Extreme (n) with the latest firmware (7.1.1) which shares it's connection with an Airport Express in the next room. I have an iMac G5 (the rev. right before the iSights) and a 12" Powerbook (final rev.).

Yesterday, I went to use DropCopy (1.3.2) to transfer a file from my desktop iMac to my laptop PB. I opened it on both as I've done countless times before, but to my dismay, it wouldn't send the file. It would say "'Connecting.." then give me an error saying it couldn't connect and to make sure port 5052 was open or something like that. I CAN send a file through DropCopy from the PB to the iMac, but not from the iMac to the PB. There is also a G5 tower in the room which does the same-I can send to the G5 but not from the G5 to the PB. The PB comes up as a location with no problem, but it won't send to it. If I add it's IP as a location manually, it will send the file, but I'd rather not have two redundant entries if possible.

So, I tried File Sharing. I turned it on in Sys Pref, and went to the iMac's Finder>Network>and then 'Powerbook G4' (original name, I know) Pressing Connect yielded another error. It said the server is not operational. If I try to connect again and again, it seems to connect on every, maybe, 4th or 5th try. I can connect to the iMac from the PB via File Sharing with no problems. Do you have any idea what may be going on here? It seems like my PB is just being cranky and refusing to take gifts from others. Is there any way to reset Bonjour? The thing is, the name Powerbook G4 pops right up in both DC and FS, so the computers are seeing it, they just aren't connecting to it well.

Thank you for any insights or suggestions. (I did try the cursory restart, as well as a complete Maintenance routine via Jesse Hogue's Maintenance 3.6 thinking that couldn't hurt, but alas, no go.)

Oh yeah, I do not have the firewall enabled on any computers.

So I did some more testing and I've narrowed it down to the network. If I hit "Renew DHCP Lease" in Sys Pref>Network on the Powerbook, DropCopy will send a file to it. A minute later, it won't work again until I hit the Renew DHCP Lease button again. Is there some way to fix this? The Airport has the default 4 hour setting for DHCP. Help?

 

Paragraphs, check. Sorry.

I forgot to mention that the firewall isn't even turned on, but good guess.