Empty Cell Validation

[Guest]

I have a cell in worksheet that needs to be filled in prior to closing file
OR clicking control to be directed to secondary worksheets. Data validation
only provides error messages upon entering a value; I need an error message
if the cell is overlooked. TIA for any help,

 

[Guest]

I think I've found the correct code. How's this?

Private Sub Worksheet_OnExit()
If Sheet1.Range("A91") = "" Then
MsgBox "Please enter contact information at bottom of form."
End If

End Sub