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Well, can't tell you why you are getting that message I can say do not use Look-Ups in Tables. Have a look at...
Lookup fields in tables are a feature provided by Microsoft that causes a lot of confusion, see…
http://www.mvps.org/access/lookupfields.htm
You can use what we like to refer to as *Look-Up tables*. Look-Up Tables are simply regular tables that hold lists of values for use in Combo Boxes on forms.
That said, if you still want to use them, please post the exact error message you are getting and exactly what happens along with your Access version.