I had this problem too, did you manage to find out more details about it?

Public Sub save_book()
    ' fasctinating.. cannot use .protect methods when
    ' using thisworkbook.save
    Application.SendKeys "^s", True
    DoEvents
End Sub

The above code will press keyboard short-cut CTRL+S. DoEvents allows the operating system to recognise the save before moving to the next part of your VBA code.

Not sure if excel allows you to change keyboard short-cuts though!