"Bad Request. Your browser sent a query this server could not understand"

[Paxinou]

I've got a mystifying problem. This problem occurs ONLY on one Mac...a 17" 1 GHz Powerbook; I have no such problem with another Powerbook that I have, an old 667MHz Ti nor with any other computer.
I can no longer log in to an account that I have with a major bank. No such problems for several years; it began just a couple of days ago, and ONLY on this particular computer. When I attempt to log in, I am informed, "Bad request. Your browser sent a query this server could not understand". I don't have this problem when logging in at any other bank...or credit card account.
I get the identical message regardless of the browser I use; I've tried logging in using Safari, Firefox, Opera, Demeter, and iCab.
I've tried everything I can think of: running DiskWarrior, TechTool Pro, repairing permissions, purging all caches, repairing disk in Disk Utility off my installation CD...everything normal there, no repairs reqired. I've even tried connecting my Powerbook directly to my cable modem, bypassing my router altogether.
Other than this one issue, everything's going smoothly on the recalcitrant Powerbook.
Anyone have any ideas? I'm totally flummoxed.
I'm running OS 10.4.9

 

[gege]

are there any answers to this problem? have the same!

 

[Paxinou]

I discovered if I created a new user account, the problem didn't occur there; it only occurred in my administrator account!
I then decided to upgrade, very belatedly, to OS 10.4.11. Well, not only did the problem persist....no go in my administrator account but no problem in my new user account, I now had an additional problem; my Demeter browser would crash instantly upon launch, every time. And, once again, only in my administrator account, not in my new user account.
I finally got totally disgusted with this whole thing and bit the bullet; I backed up my hard drive and did an erase and clean install of my OS. I was reluctant to do it because that means a time consuming process to get everything totally back together again.
But after doing the erase/install, and upgrading again to OS 10.4.11, I now have no more problems! I can once again log in to my bank account, and Demeter doesn't crash. I don't need to create a new user account. Everything's running smoothly once again. My earlier problems were, apparently, due to something becoming corrupted somewhere in my OS.