No argument from me re the sharing of an FE, but this error also has a known cause. What I don't know is, if that cause results in the error every time, or just sometimes, depending on conditions. That cause is having a load event on a subform that references the parent form. This can be an issue since (as some of us probably know) the subform opens first, thus it's load event fires before the main form is open - thus the reference to the parent form cannot be resolved. It goes looking for the object or property being referenced, and returns without finding anything. This is just another one of those cryptic errors that aren't distinctly identified. What's missing of course, is the old Return command from BASIC, which is where this error message stems from.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.