Minor change...

Replace B2+1 with ROWS(Data)+1

Hope this helps!

In article ,
Domenic wrote:

First, assuming that Sheet1, Column A, starting at A2, contains the
data, change the reference for the defined named 'Data' to...

=Sheet1!$A$2:INDEX(Sheet1!$A$2:$A$65536,MATCH(9.99 999999999999E+307,Sheet
1!$A$2:$A$65536)+1)

Then, let B2 contain the number of interest, such as 30, and try the
following formula which needs to be confirmed with CONTROL+SHIFT+ENTER,
not just ENTER...

=LOOKUP(2,1/(FREQUENCY(IF(Data=B2,ROW(Data)-MIN(ROW(Data))+1),IF(Data<B2
,MATCH(ROW(Data),ROW(Data),0),B2+1))=2),ROW(Data))-1

Note that if you'd like to check for the last instance of 3 consecutive
values, change =2 to =3, and so on.

Hope this helps!