RewriteCond %{HTTP_COOKIE} not working

Hello. I'm trying to create different views of my website based on a
cookie. I've confirmed that the cookie is being set correctly, but
when I try to access a page my rewrite rule isn't matching:

# dev view
RewriteCond %{HTTP_COOKIE} ^__view=dev$
RewriteRule ^(.*)$ dev/$1 [L]

When I comment out the RewriteCond rule, and access http://mywebsite/
it works fine, rewriting the url to the dev/ subdirectory. When I
uncomment it, apache says I don't have permission to access / on this
server.

I've checked in Firefox's preferences panel and view php that the
__view cookie is present and that the value is dev.

I'd appreciate any help - this is for a client and I'm past the
deadline.

I solved the problem. It turns out it was not the rewrite rule. I
don't understand exactly how this works, but the script setting the
cookie was in a subdirectory, and the .htaccess file with the
RewriteCond rule was in the parent, so for some reason the cookie
wasn't there when the .htaccess file looked for it, so the rule was
legitimately failing. I checked this with a script in the parent
directory - the cookie wasn't there, though it was there in a script in
the subdirectory. I guess I don't quite understand how cookies are
mapped to domains - I suspect that the other rewrites I'm doing are
having an effect on what domain the cookie is stored under.

In short, for the moment the solution is to move the cookie-setting
script into the same directory as the .htaccess file looking for it.