Does the report work fine in the designer?

>Ok, I found the merge modules. All is ok except
>for on thing.
>
>I'm getting a message "This field is not known" when
>I run my report.
>
>The report was ok in CR 8.5, and now I get this
>message.
>
>It appears the say that there is an unknown field. But
>WHAT field??
>
>Any idea what this is and how to stop it?
>
>Thanks