I had the same problem so on the workbook_open event I put this code:

If Me.ReadOnly Then
       Result = MsgBox("Are you sure that you want to open this spreadsheet
in Read_only? You won't be able to save any changes that you make!",
vbCritical + vbApplicationModal + vbYesNo, "Read-Only Warning")
       If Result = vbNo Then
           Me.Close False
       End If
   End If

That way the user gets a second box telling them what is happening.

Rui