The problem account may not have access to the dataset specified in the Custom Command field found on the Connection tab of the system.
The check password process uses the setbutteraddress command to check that the password is correct. It will set the buffer address to the value found in the Custom Command field.
TPAM uses a command like this when checking the password:
enter(23,27) setbufferaddress(23,23) 'customCommandFieldValue'
If the account does not have access to that dataset an error like this will be presented:
field(protected,intensified) 'testUser userid logoffb% not authorized to use customCommandFieldValue ' setbufferaddress(3,1) startfield(protected,intensified) ' ' setb