PTO hard to engage or cannot engage

Hello all I have a 63 1010 RU that I just got running and 5' bush hog. Yesterday I hooked everything up fired up the tractor and tried to engage the PTO and it would not lock into place, after a couple minutes of going around the field holding the pto lever in one hand and steering with the other the PTO lever snapped forward and locked into place so I finished cutting the field I was in. I then dis-engaged and moved to my second field where I could not get it to lock back in again. I quit and took the tractor to the barn and gave up for the night. Are there any adjustments I can do for this or are there any other sujestions.

I'm not too sure about this.... Does this happen when there is no shaft connected? Reason I ask is some times mine will bind up a little bit with the bush hog. If it happens again try disconnecting the shaft/or spinning the shaft then try it again.