You probably have one or more gigantic procedures/functions and I think VBA has a limit of 64k or something per procedure.
You fix it by splitting that procedure up into multiple procedures that can then be called by the one procedure.
So instead of having:
Sub GiantProcedure()
... ' lots and lots of code
End Sub
You’d have something like:
Sub GiantProcedure()
... ' a little bit of common code
Proc1()
Proc2()
Proc3()
End Sub
Sub Proc1()
... ' quite a bit of code
End Sub
Sub Proc2()
... ' quite a bit of code
End Sub
Sub Proc3()
... ' quite a bit of code
End Sub