This is just a hunch, but it seemed to work when I tested it on my machine.

Try to mark the template file as read-only.
1) Right-click on the file (in Windows explorer)
2) Choose Properties
3) Check the Read-Only box.
4) Close the properties box
5) Test it out.

The reason I think this will work is that a template file is opened as read/write once you open on of the files created from that template. My guess is that this is done so that if you modify one of the template features (style, header, footer, etc) then you can save the changes back to the template at the same time.

When you want to modify the template, which is probably fairly rare, just mark the template writable for the short period of time that it is actually begin modified.

Good luck
Paul