Just change the first Comma to Colon (:).
=COUNTIF($F11:$AN11:$AR11:$BF11,AN11)=1

But in your formula you are including the AR11 in your Countif Range and
again mentioning the same cell as Criteria (AN11)
=COUNTIF($F11:$AN11:$AR11:$BF11,AN11)=1

I think it should be like the below:-
=COUNTIF($F11:$AM11:$AR11:$BF11,AN11)=1

Remember to Click Yes, if this post helps!

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(Ms-Exl-Learner)
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"Gotroots" wrote:

Hi

Could someone be kind enough to tell me what is wrong with the following
formula

=COUNTIF($F11:$AN11,$AR11:$BF11,AN11)=1

Thaks