Post this over @ guntalk-online
Also Go to the rimfire handgun area & read away @ MKIII Troubles..
I've heard of this happening before but have never had this problem with any of the half dozen MKIIs I've owned..
I think you'll find your hammer strut is not in the mainspring correctly..
IIRC I've read were some folks had to remove the grips & drive out the sear pin in order to resolve some assembly problems.. You may also be able to manipulate the sear and/or hammer threw the slots on either side of the gun under the grips, use the propper screw driver as not to ruin the screws..
When assembling the mainspring back into the gun you have to make sure the gun is not cocked, hammer forward & that the hammer strut is aligned so it can drop into the mainspring as you swivel it up into place by turning the pistol upside down barrel up while assembling..
Good Luck & Don't let this get you all flustered..
I have a buddy with three MKIIs & always am the one who takes them apart & cleans them & re-assembles them for him..