When adding a user defined field to a screen in the past, I sometimes got errors when the field ran over the size of the form or frame.  Not sure of the exact error message when that happened but seeing the word position in your description is making me think that might be the case.

Kevin,

The fields which are being reported in the error are indeed off screen.

During Sales Order entry, if a part number is entered which does not exist in the item master,

the user can choose to enter the part "on the fly". This is where the error is generated.

The same form is used during part entry/edit when accessed through Item Maint without an error.

Why is the Sales Order route to Item Maint creating the error?