Message Pop Up if cells in a Column already have a "True" value

[vwong688]

Hi,

Can someone help me write out a vba script for a pop up message for Collumn E if the cells in that column already have a TRUE value?

Collumn E is check boxes in a checklist spreadsheet I am trying to make. I am trying to put in a warning message if the user is attempting to check something off twice.

Thanks!