How do I update a field in a sub-form when the main form is data entry?

[RAIN63]

I have a mainform set to data entry to add records to TABLE1. I inserted a subform that shows fields from TABLE2. I have a field in TABLE2, let's say TBL2FLD1(NUMBER). I want to add TBL1FLD2(NUMBER) from TABLE1 in the mainform to TBL2FLD1 and update said field in TABLE2. My problem is: (1) I get a #TYPE! error when I try to add the two fields, which I have tried many, many ways (adding them together in the Default Value; creating an unbound field to hold the calculation and then putting that field into the Default Value of TBL2FLD1; ETC), and (2) I don't know how to get the subform to update TABLE2. It seems like the control gets stuck in the subform. Is there a way to accomplish this without coding it?

[June7]

These are the pk/fk fields that relate the two tables? Make sure they are same data type - pk/fk fields must be same data type. If pk is an autonumber then the fk must a number.

Then set the subform container control Master/Child links properties to the pk/fk fields.

[RAIN63]

No, they are not the pk/fk fields and yes they are the same data type. The links are set to the pk/fk fields.

[June7]

Then I don't understand what is happening. Want to provide db for analysis? Follow instructions at bottom of my post.