A while back Photobucket made everyone re-enter a new password. If you haven't used it recently and didn't go through this procedure, that might be why. I think there is a place on the log-in page where you can request they send you the password to your email. Then you might be able to enter a new one after that?
Also, I have found a glitch with Photobucket. If I type in my username and then tab over and my password fills in by itself with the little stars, it sometimes won't accept it. So I type in my username and then tab over and then erase the stars and then retype my passord myself and it works. I have no idea why. Hope this helps.