Workbook BeforeSave Event causing workbook to close

Hi

I'm trying to create a workbook which users update then send via a separate command button to the 'data collector'. I'm trying to build in that they can't save the workbook, only the 'data collector' can.
I've added in the below event but when the user clicks OK on the message box the workbook closes, what I'd like it to do is when OK is clicked the user returns back to the workbook so they can 'click the send button'.

Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
If Environ("Username") <> "jrussell" Then
 Cancel = True
 MsgBox "You cannot save this form, click the Send button instead"
End If
End Sub

Can anyone see where I'm going wrong?

Thanks!