Can be both or either.
Not a stupid question! The error message does not discern the root cause (usu seen in Static studies). The problem is, there is something "loose" in the assembly. This can be caused by any component where A) it does not have a Bonded Contact set to another component or ground, and/or B) there are not enough restraints to hold it (from the "Fixtures" folder). To find the offending component, go to Study Properties, switch on "Direct Sparse" solver, and check "Soft Spring Option". Then, run static and plot displacement at some scale other than one. You should be able to identify the loose part by the red color. Sometimes loose parts go out of view, so you can plot at zero scale (no deformed shape). Hope this helps.