Setting primary key fields to not accept 'Null' values

[Fons Verbeek]

I am working on an information system with MS Access (2003) as front-end and MySQL (5.021) as back-end. Tables link good via the ODBC connector and data can be inserted, updated and deleted. The problem which has been bothering me for some time now is that I cannot set the primary key field to not except ‘Null’ values.
Both in the table view and in the form I created the table will except ‘Null’ values for primary key fields, even though in the table design view in Access I can see that the ‘Required’ property indicates ‘Yes’.
The ‘Allow zero length’ property on the other hand also indicates ‘Yes’, but none of these are changeable from within MS Access.
I’ve tried to set validation rules (Is Not Null) but this doesn’t help either.
The MySQL Administrator tool indicates that the field has the 'Not Null' property.

Does anyone know what the cause of this problem is and how to fix it or work around it?

Thanks in advance for any helpful comments!