What is index key expression for the TAG in question?

>In a new app I am appending a table ctreated in VFP 9.0SP1 to a table created in VFP 8.0. I get an error (Error building key for "table name" tag "tag name". Error 2199.
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>The table structures are exactly the same, same # of fields, same field lengths, and same field attributes. The table created in VFP 9.0SP1 has no indeces, however.
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>Are there compatabliity issues between the two versions? BTW, there are no memo fields in either table.