In Insight Sysview for DB2 just started receiving this message when trying to view threads:
DBG55036W Request THRDACTV is not found. You selected a view whose request is not available. The "Detail Yes or No" question on the Start Qualification panel controls the starting of one of the probe's components.
It's likeley that THRDACTV is not running. To verify this check the datacollector job output and do a find on THRDACTV. If confirmed that the request stopped, then issue the Start THRDACTV from Insight main menu or the list panel to start the request.