Incorrect password or not a TrueCrypt volume

[Darknight]

I'm getting this error on two volumes I created in windows some time ago, I have some more of them but until now I have tried only these two. Nothing makes me think that I'm getting the password wrong, at least not like 30 times in a row on two different files...
What I noticed is that if I modprobe truecrypt after the third password try the truecrypt module is gone from memory.
This may be a symptom of something going wrong with truecrypt, even if the logs say absolutely nothing.
Clues? Thanks!