You are right with the typo (rather omission from my part to “update” Evan’s code after paste), but the idea was obviously the same with what you suggested.
Your comment confirmed that Evan’s code did what he said, so I thought (still missing the typo...) you were talking to him...

>Yours:
>dimension laSearchFields[n,m]
>laSearchFields = thisform.aSearchFields
>DO FORM FIND WITH "device", thisform.aSearchFields TO lnid
>
>Typo Corrected:
>dimension laSearchFields[n,m]
>laSearchFields = thisform.aSearchFields
>DO FORM FIND WITH "device", laSearchFields TO lnid