The problem occurred because Thread Termination/Dynamic DSNZPARM (PTT) does not support pageset names values containing the '*' wildcard character.
The -STOP DATABASE command worked correctly. But after the -STOP DATABASE command had been issued, Thread Terminator looked for a pageset named '*' but could not find one. Since Thread Terminator was unable to find the pageset name specified, it also could not find or terminate the threads using the pageset. Since the threads had not been terminated, the status of the pagesets was stop pending (STOPP) not STOP. The -START DATABASE command failed because the -START DATABASE command cannot be issued successfully until the threads using the pagesets have terminated and the status of the pagesets has changed from STOPP to STOP.
You should be able to use the "Thread Terminator Terminate Pageset Users" display successfully provided that you specify the full pageset name.