Still need help updating from a form

[qurn]

I have 3 Tables One named "bulliten" one named "whomakes" And one that combines the 2 named "bulrid".

I have a form with source "Bulrid" Who makes is chosen with cascading combos, and the bulliten information is suppost to be filled with a subform. but every time I try to put some info in the text boxes I get this error

You can't assign value to this object
*the object may control on a read only form
*the object may be on a form that is open in design view
*The value may be too large for this field

I checked that the value is not too large, and the form is not open in design view. I don't know how to check for the first one, but this is the only instance in which I use this particular form.

Emmediately after clicking OK I can input things into text boxes, but the Auto number doesn't fill in its related field.

 

[qurn]

Alright I found out this can happen if you have the ID field in your subform. now I'm getting error message

You tried to assign the Null value to a variable that is not a Variant data type. (Error 3162)

I'm going to read up on this, but I don't see why I'm having this problem.