is the suspension displacement that you are setting very large, enough to get to the bump stops? if you run 50 bump -50 rebound (mm) instead does the error still appears?
So the actuator error makes sense; there is a force limit induced in the testrig, since the suspension goes into bump stop the actuator force gets too high and fails (like a safety device). Step size too small may be that Adams is reducing the timestep too much to get it working and eventually fails.
Conclussion the testrig works if you set sensible numbers (+-50), I'm not sure what is the intention of going into the bumpstops region
