Password Change: ErrorCode 20

Hello, some user try to change her password but the system response with: Errorcode 20, looking at log file management-console-web-server.log:

30.10.19 11:40:34.364  MAIN        ( PROCESS ) : CPSet (172.20.192.11:38522) response status code: 400
30.10.19 11:40:34.364  MAIN        ( PROCESS ) : CPSet (172.20.192.11:38522) response message: Changing password failed. The reason could not be determined. In case it helps, the raw error message will be displayed: Errorcode 20: The new password could not be set.

what does it mean?

Ps:

# lsb_release -a
No LSB modules are available.
Distributor ID: Univention
Description:    Univention Corporate Server 4.4-1 errata223 (Blumenthal)
Release:        4.4-1 errata223
Codename:       Blumenthal