repeating cells

[Kevin]

Hi, is it possible to have an error message pop up when info in a set of 2
cells repeats? For example, a2 & a3 contain Joe and apple. I'd like an error
to come up if that exact info comes up again in a5&a6, a8&a9, a11&a12, or
a14&a15. So basically, I don't want to be able to repeat the info in those
cells next to each other as shown. Also, I will be using drop down lists in
those cells if that changes anything. Thanks for any help.

 

[David Biddulph]

=IF(A4&A5=A$2&A$3,"Error","") in B5, and copy down.

 

[Kevin]

Thanks for the reply David. That works fine but I need it work on any if the
cells listed. I would like an error if any of the double cells match each
other, not just a2&a3 if possible. So, if 5&6 match 11&12, error, etc.. Also,
is there a way to address the using of dropdown lists in this case? I tried
the formula in the conditional formatting but I see it doesn't work unless
the cell info is typed in manually. Thanks again, -Kevin