If you look at the form's Properties, what *is* visible in the On Load event?
It should be literally and exactly

[Event Procedure]

It's also possible that your database is corrupted. Have you tried Compact and
Repair, or decompiling? If you don't have a backup, *MAKE ONE NOW*; and check
the suggestions at

http://www.granite.ab.ca/access/corruptmdbs.htm

            John W. Vinson [MVP]

You can get that error if you change the procedure declaration
for one of the form or control events. For example, change

Private Sub Form_Open(Cancel As Integer)
   MsgBox "Hello"
End Sub

to
Private Sub Form_Open(Cancel As Integer,fred, fred)
   MsgBox "Hello"
End Sub

Access exposes a (callback) property which allows you
to attach methods to events. If you put [event procedure]
into that property, Access calls a standard method, using
a standard naming convention (The property is an unusual
Access property, which most ole objects don't have. Most
OLE objects just call standard methods, which you can
supply. You see this when you drop an OLE object on to
a form: most OLE objects have methods in the VBA window
which are not shown on the Access property sheet)

If you have another procedure with the same name as the
standard procedure,  but the procedure declaration does
not match, you get this error.

However, I would assume that a likely cause of this error
would be corruption of the compiled code. Even if your
source code has the correct declaration, if the compiled
code is corrupt, the compiled signature might not match
the calling signature. Decompile would probably fix that
problem.

(david)