I have prevented duplicate entries in a column containing numbers using data validation. when trying to enter a number which does not exist in the said column, error message displays and entry is prevented. Please help
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Either remove the data validation or show us the formula you used to do that data validation.

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Andrew Lockton
Chrysalis Design, Melbourne Australia

Thank you for the prompt response and help. I have used the following formula:
=COUNTIF($E$3:$E$20000,E3)=1

Thank you once again.

This reference's method works for me
Excel formula: Data validation unique values only

Allow = Custom
Make sure you are ignoring blanks
Try <2 instead of =1

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Andrew Lockton
Chrysalis Design, Melbourne Australia

That worked. Thank you very much for the help