I had the same problem on another Gottlieb EM. For the life of me I could not figure it out. It started when I was playing the game and tilted. I tried to reset the game but nothing happened. It just kept saying Tilt. I looked at everything. I then brought in a technician to take a look at it. After a few minutes he got the machine working.

The issue was the tilt mechanism was stuck. The tilt weight was at at depth where it got caught under the brass tilt plate. I felt pretty stupid. Especially since I knew exactly when the error occurred and never looked at the tilt mechanism. But I am pretty new to this hobby, so a good learning experience.