Thanks... this is great..... it does fix my problem... I put it into my file
and works great.... have one more question... is there a way to do it not
using arrays..? they are great but I am NOT well knowledgeble of them and
limit some of my capabilities to do some other validations.

"Bernd P" wrote:

Hello Alberto,

Array-enter into D1:
=MAX(FREQUENCY(IF($A$1:$A$4=A1,$B$1:$B$4),IF($A$1: $A$4=A1,$C$1:$C$4)))
and copy down to D4.

Please notice that you need to array-enter this (enter with CTRL+SHIFT
+ENTER, not only with ENTER!).

All resulting numbers should be 1. Any higher number than 1 indicates
an overlapping range for the corresponding date code.

Regards,
Bernd