Every now and then you get an error:
"Unable to update the
password. The value provided for the new password does not meet the
length, complexity, or history requirements of the domain."
So you need to find out the allowed length in the password policy.
An easy way to do this is to run:
Other reasons for this message are that you have already changed your password in the last 24 hours or that you have reused a password that you used in the last 24 passwords.