Excel: Data validation... Help needed!

Hello, I'm making an excel database with email adresses and phone numbers. I wish to receive an error alert whenever a phone number has already been put in the database. For this, I use these steps: Select cells (A2 until A20, for example). Go to datavalidation -> select custom use this formula: =COUNTIF($A$2:$A$20,A2)=1 It then prompts me I can not use '=' so I delete the equal sign (is this normal?) I test the first cell and any number or value I typ in, it gives me an error alert. [IMG]http://s18.postimg.org/w30xf1qp1/Data_validation.jpg[/IMG] [IMG]http://s18.postimg.org/4r5odplyd/Data_validation_1.jpg[/IMG] I do not understand what is going wrong. I tried installing an older version of excel because I thought it might be some bug, but it's the same result... I use Office 2010 atm. Help pls! Regards, pthdz

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This thread is current as of February 24, 2014.

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