From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3)
Description of problem:
If a user tries to change his password via using userpasswd and
mistypes his current password, the program gives an "Unknown error."
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. go to Main Menu / Preferences / Password
2. When prompted to enter the current UNIX password, intentionally
Actual Results: "Unknown error" dialog appears.
Expected Results: It should say that the user mistyped the current
UNIX password and offer another try.
this bug is still present in usermode-gtk-1.74-1
this bug is still present in usermode-gtk-1.79-2
This is now fixed since useermode-1.80-1.
The error was caused by the unhandled PAM_AUTHTOK_ERR error code.