To add to David's answer, this applies not only to lists but to combos too. You can get this error if there's any typo in the list of fields you've specified for the RowSource, or if the alias you reference with the first field isn't open in the current datasession.
>Microsoft Visual FoxPro
>OK
>Help
>'field' phrase is not found.
>
>Hello all
>
>I'm getting this error message,and i have not issued anywhere prompt in my program,what could be wrong.
>
>txs