Thanks , but I got the message:

The formula you typed contains an error..

Did I have to change M to the empty cells in L, in the second part?

"Harlan Grove" wrote:

Outlook, eh? wrote...
....
=IF(M2="","","ImportId-"
&TEXT(SUMPRODUCT(--ISNUMBER(SEARCH("Import",$K$1:K1)))+1,"00"))
....

Maybe try

=TEXT(SUMPRODUCT((TRIM(M2)<"")*(2TRIM(M
$2:M)<"")),"""ImportID-""00;;")