Can't enter null in combo box

[kballing]

I have a form with many combo boxes that correspond to various answers for a survey. The fields are integers that correspond to various answers.
e.g. 1; "very good"; 2; "good"; 3, "fair"; 4; "poor"; null, "N/A"
I have the row source as shown above. (however not all combo boxes have the same answers available)
I get an error "The value you entered isn't valid for this field." whenever I try to select null; "N/A" from the combo box.

How do I make this work so that null is an acceptable option?

 

[pbaldy]

In the table/field the combo is bound to (control source), is that field set to required?

 

[kballing]

no. not required. I've done the same thing with other combo boxes without a problem. I just can't figure out what's different.

 

[smig]

what you'r doing is a bit risky.
this way you'll never know if the user selected the "N/A" as intended, or simply moved to the next field.
I suggest you give the "N/A" a real value. it can be 0.

 

[kballing]

@smig, I guess you're right, there's no reason I can't set N/a to be 0. That's what I'll do.

Still, if anyone can shed some light on this, I'm still curious as to why you can't make null a selectable option, or at least some suggestions for my particular circumstance.