Hi
If you are in EHP upgrade and in Execution phase where the system is locked and no other users are allowed to login except DDIC then use the following command to unlock your system
tp unlocksys <SID> pf=<DIR_PUT>/var/DEFAULT.TPP
you can find DIR_PUT value in your DEFAULT.PFL file in profile folder
This is basically your SUM/abap folder.
Make sure to lock the system after your task is done in other client before proceeding to upgrade again.
Thanks
Rabi