"Return without GoSub" when using subforms in Access

This can occur when there is a Form_Load() event in the subform, but not the main form. Try adding an empty Form_Load() event to the main form.

The most likely reason for this error is that the project has become corrupt. You should decompile, instructions are here: Debug a bad DLL calling convention error

First, ensure that you have switched off Name Autocorrect: http://allenbrowne.com/bug-03.html and ensure that you are not missing any references.