MasterPW wont let me change filevault accPW

I forgot the password for my file vault protected account. (Snowleopard MacBook)
I have the master password, and it "works":
I click "reset password" at the login screen, type in the master password, the message about the keychain appears but when i type in the new password (i tried different ones and i´m shure i repeated it correctly) the box shakes, like it does when you type in a wrong password..

Theres only this one filevaulted account and I don´t have the installation dvd here.

Any ideas?

The master password to your account is not the same as the one which you assigned to Filevault unless you just happened to assign the same password to both. There is no way to change it without the original.

If you forgot the Filevault password, your data is toast. There is no way to recover. And since you don't have the original install DVD, you can't reinstall OS X.

A couple of hard learned lessons here: Unless you have atomic secrets on your machine that you're trying to protect, don't use Filevault. And always keep your install DVD on hand.

If you need to get into your machine right away, go to the nearest Apple store or Best Buy and buy a copy of Snow Leopard for $29. That will work unless it's a 2011 MBP or iMac.

Struth this Filevault is a dangerous tool. Wonder why innocent folks ever invoke it?

"The master password to your account is not the same as the one which you assigned to Filevault unless you just happened to assign the same password to both. There is no way to change it without the original."

But I HAVE the file vault master password - the one i created when I turned on filevault. And thats the one I´m asked to type in to change the account password.(I know because of the hint) It´s only on the NEXT SCREEN where it reads New Password / Repeat / Hint (optional) that it wont accept any new password!!

Ok maybe my description was missleading.. So here´s the long version:

Step 1: I turn on mb. Loginscreen apears.
Step 2: I click the button "Reset Password" OR i enter a wrong password three times
Step 3: the loginscreen now says:

Master Password: [input field]

Type the master password to reset this users password and to unlock FileVault.
Master Password hint:
*****​

Step 4a: I enter a wrong master password -> screen shakes "it off"
Step 4b: I enter the CORRECT master password
Step 5: a message apears:

If you change the password for this user account, you will create a new keychain to store the users password. The users previous keychain...​

Step 6: I click OK
Step 7: Screen now says:
New Password: [____________]
Verify Password: [____________]
Password Hint: [___________ ]
(recomended)

Step 8: I try to enter a new password, always extra careful to verify correctly but no mather how long, or difficult, with or without hint the screen alway shakes it off like it does with wrong passwords.

I know not remembering the account password is my mistake, but unless I´m missing something here this would be the worst glitch I ever heard of... like the filevault-feature should´t even be there. There just has to be a way around this.
Needless to say the data on this account is pretty important.

This is only a guess, but you may not have enough disk free space.