Custom error message under picklist

Question

Currently the validation error is a predefined message for the custom picklist Banner__c.

.

I wrote the following validation error to create custom error message.

It seems to be an esay task, but nothing is woking in my case. Still the predefined error message is coming. I tries the following rule for this.

ISPICKVAL(Banner__c, "")

ISPICKVAL(Banner__c, "NULL")

ISBLANK(TEXT(Banner__c))

TEXT(Banner__c) = ""

Answer 1

Uncheck the box on the Picklist field edit screen that requires a value.

Edit: Also uncheck the box on the page layout editor that makes the field required.