On Mt.Gox Claim site
The password for this account is invalid, or this account is not currently under claim process.
I was getting this since yesterday morning.
Basically, THE NEW PASSWORD IS TOO SHORT.
I was using a 15 character new password and I was getting this error. Today,after trying a few times,it hit me, and I used a 28 character "new password" and it worked with no problems.
at least this worked for me.
I posted this in another thread but I thought I should make a new one for people to see, because I see many people screaming about it.
edit: I am 100% sure that I was entering the right "old" password the first 100 times I tried, but I was always using a new password of 15 or shorter. the first time I tried with a long password, it worked.