Update the sapstartsrv and restart the service.
Check these notes for additional reference.
1895278 - SUM fails in INPUT-OS-USER-PASSWORDS phase .
Also make sure the permission and ownership of sapuxuserchk are set as suggested in this SAP note - 927637 - Web service authentication in sapstartsrv as of Release 7.00
Finally repeat the phase on SUM.
Regards
RB