This is a common instability error from the program. It means there is rigid body motion from the new body you inserted (for similar to what was happening here: Model geometry might be changed -Simulation). Did you apply specific bonded contact sets to the newly inserted body? Did you run any stability checks with the study?
I used method 1 and 3 of the page you linked to figure out which component was giving trouble. after that i saw that that component had multiple bodies. (fixed this by checking the "merge result" at certain features)
then i applied contact sets for every component in the assembly and now the simulation was a succes!
So thank you very much for your reply!