Error 1 attempting to set userid to "Abc": AHD05910:User ID entered needs to be unique.Multiple Active Contact records with the specified User ID credentials were found.
This issue occurs because there is a code (force_unique_userid.spl) to validate that the userid's are different. I can see the following in the log when testing with user spadmin to Spadmin:
spelsrvr 7592 TRACE force_unique_userid. 63 old_val='spadmin' new_val='Spadmin' userid_escaped='Spadmin'
spelsrvr 7592 TRACE force_unique_userid. 78 found 1 UserID's that matches 'Spadmin'
spelsrvr 7592 TRACE force_unique_userid. 82 'Spadmin' UserID already exists
Release : 17.3
To avoid this issue there are 2 options:
1. workaround: change the userid to something different (ie: abc1) > Save changes > change to Abc
2. Install the option named "ignore_security_case" under Options Manager > Security > Restart SDM services. Reference: