Can't assign a value to this object (1 Viewer)

Greetings, all.
Run into a snag with a payroll db, appreciate any help you can give me.

Main Form, with ordinary payroll/personnel info--clock no, first and last names, S.S.no., etc.
Subform for entering regular hours worked, OT hours worked, etc per Period Ending, keyed to main form by SS no. Pretty basic stuff.

Problem is, when we try to enter the first data in the subform, we get this error message :
"You can't assign a value to this object.
*The object may be a 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."


We get the message in the first field we go to, no matter which field we go to first.
None of the "may be" conditions apply.

When we hit "OK" the message goes away and we can enter our data, the records are created corrected. But as soon as we move to the next record, we get the same error.

Any idea why we're getting this error message?

Thanks for looking,
BeckieO

Never Mind

Sorry, turns out the SS no field in the subform had a calculated value, instead of a link.
Not sure how that happened, but that was the problem.

Thanks to all, anyway,
BeckieO