:-)
From previuos post I see that you didn't need of Clienti at all:
Just change

* from:
      where contatti.codcli == clienti.codcli ;
        union ;
          .....
            where agenda.codcli == clienti.codcli and Empty(idc);
          ......
*to:
      where contatti.codcli == wanagraf.CODCLI ;
        union ;
          .....
            where agenda.codcli == wanagraf.CODCLI and Empty(idc);
          ......

Also, are you using IDX instead of CDX? I ask becuase of that line:

Set Index To 'clienti1'



>I got through the error with the Try...endTry set of instructions :
>

>	Try
>		If !Used('clienti')
>			Use clienti Again In 0
>		EndIf
>	Catch to oErr
>		If oErr.errorno = 9
>			If !Used('clienti')
>				Use clienti Again In 0
>			EndIf
>					
>		EndIf
>	Finally
>		If Empty(Sys(14,1,'clienti'))
>			Select 'clienti'
>			Set Index To 'clienti1'
>		EndIf 	
>	EndTry 	
>

>
>Now it goes on without errors but I don't like this solution very much...