Replacing too many logical statements in IF-ELSE Condition

Why not check them one at a time?

If one of them doesn't have valid input, tell the user, return focus to the offending textbox and exit the sub.

For I = 1 To 14
    If Me.Controls("TextBox" & I).Value = "" Then
        MsgBox "Input required in TextBox" & I & ".", vbCritical
        Exit Sub
    End If
Next I

' if code execution reaches here all the texboxes have been validated and we can proceed