Problem with Tomcat's action

My Beretta Tomcat recently developed problems with it's action. When in the double action/hammer down mode, the trigger will engage the trigger bar, but the trigger bar will not engage the hammer. Therefore, the trigger in the double action mode will not cock the hammer unless the trigger bar is manually pushed from the side while squeezing the trigger. Single action is no problem. When manually cocked, the trigger will drop the hammer without malfunction. The problem started immediately after I disassembled the grips while cleaning the pistol.

Could it be an overstretched spring? Was it something I reassembled backwards? Is it a worn-out trigger assembly? Is it a simple problem that could be handled by a local gunsmith, or is it something that would require returning the pistol to the factory?

"A fear of weapons is a sign of retarded sexual and emotional maturity."
Sigmund Freud, "General Introduction to Psychoanalysis".