You have to specify which index to use for seek. The best way is to use SEEK() function

IF SEEK(addition.name, "addition", "IndexTagToUseForSeek") 

>	USE ftab                   &&added by me
>*	SELECT ftab 
>	
>	USE addition              
>	SELECT addition             
>	SEEK addition.name  &&check for name 1st
>SCAN &&added my me
>	IF FOUND()
>	THISFORM.UpdateResultsWindow('error name already entered')
>	ELSE
>	THISFORM.continue
>	ENDIF
>	*SELECT addition
>ENDSCAN

>
>IT points at the Seek line