My computer/browser/ftp client loses the ability to resolve certain urls.

My gear: iBook G4 1.33 w/10.4.11

Scenario: url for resolves just fine. Upload files with CyberDuck to that domain. Works fine, at first. Then, the ftp connection times out and will not resolve. It will not connect to that ftp server again, no settings have been changed or altered. Next, the url in Firefox or Safari for also will not resolve. Other domains using Cyberduck connect perfectly. Other websites using any browser resolve normally. Transmit also does not resolve the ftp connection using all the correct settings.

This same scenario has happened with three different internet connections. At first each internet connection works fine. Then upload files via ftp, then nothing works for the domain on this computer. Other computers can view the site without a problem.

Attempted fixes:
Ran Onyx clearing internet caches, permissions, full routine. Used Software Update applying the appropriate updates including a Security update. Re-ran the 10.4.11 combo installer. No joy.

I do use a Belkin wireless usb device since my Airport card inside the iBook went bad. Don't think this is the problem since I tried an ethernet connection from the same internet source with the same results.

Any ideas? I'm in a bind since we have a big remodel project going at one of our stores and I am supposed to be doing frequent updates to our site.

Thanks in advance for any help.