Primer Problem

This is the first time Ive painted a car with pro paint and Iam having problems with the primer. I painted the primer on with my gravity feed spray gun and when i was done i took of the cap to clean it out with paint thinner and after i put all the thinner thru the gun it didnt work. A thin layer of primer was left on the walls for the cup and little chunks of it were sitting at the bottom of the cup, thankfully the gun has a filter. I had u clean it with the Urethane Activator which took almost an hour. I used Nason 421-19 2K Urethane Primer and mixed it with the 483-87 Activator, in a room around 70 degrees. Could it of been that i didnt put enough of the activator in it or to much? Thanks