I have the same problem. It started when I moved the Cardinals to Las Vegas, and the thing froze and would not let me advance to the off season. I thought it may have been a glich with the new stadium and uniforms, so I restarted.
This time around I used the Broncos. Nothing out of the ordinary, here, I stayed in Denver, lost in the SB in year 2nd year, and when I tried to move to the off season, it did the same thing as before. I did import both times, so I figure this is the problem. The issue is, I am sick of restarting the game. I play the seasons to see where it takes me, and to stop after 3 seasons sucks.
I am glad I am not the only one.