Forms Authentication + URL Rewrite Problem

Hi,
I have a problem with Forms Authentication when i re-write my urls to have the current culture in the url for SEO porposies.
for example the url: 
http://domain.my/en/about
The url rewrite role uses the server variable
HTTP_COOKIE Every thing is going oky except the Signout function of Forms Authentication when i logout the value of
Context.User.Identity.IsAuthenticated is "True"
When i stop the rewrite rule it works fine. here is my rule
<rule name="set server variables" enabled="true"> <match url="^([a-z]{2})/(.*)" /> <conditions logicalGrouping="MatchAll" trackAllCaptures="false"> <add input="{Languages:{R:1}}" pattern="(.+)" /> ...