There are plenty of places on the web you can get beginner HowTo's on Access.
These tips are subtle ones that even experienced Access developers often don't know about.
For the best Access sites on the web, check out 'Microsoft Access Links' on the Links page. Allen Browne's site is almost an encyclopedia on the subject.
Right click on the function or sub call in the code. Choose 'go to definition' from the menu !
If you select a set of controls on a form, and then cut and paste them to a different area on the form, for example when moving them out of or into a parent control, all the event procedures associated with the controls are cleared.
That's it ! All the events are now reconnected.
This solves so many problems involving this error message that it is almost ridiculous.