Seedy - 7:49 am on May 21, 2012 (gmt 0)
If you mean versions 1 to 6 then (1-6) should be [1-6] here.
MSIE/\ should be MSIE\ too. The slash should not be escaped.
Finally, RewriteRule 403.php [F]
RewriteRule !^403\.php - [F]
Thank you for cleaning that up, I was being hasty.