Alexander is probably right, but note that there are also many other ways this eror can pop up, and sometimes they are hard to find.
Firstly (as Alexander says) look at the form giving the error, compile and see if a field is missing. Second, look at the sub form (or forms if you have created any) on that form, for the same thing. If that fials, then look at the source table of the two forms, and then check it the field “entry no.” exists, but maybe is disabled. if at that point you can’t find it, then possibly you have a function that calls a field that either is deleted or inactive. The easiest way to find it is to use the debugger, and let it stop at the error.