ISAPI Rewrite won't proxy the root folder

I wasn't sure if this is a ServerFault question or StackOverflow, so I am going to ask it here first.

When using ISAPI Rewrite (Helion Tech), I cannot seem to proxy the root directory http://www.somesite.com/

http://www.somesite.com/subdir/ will work if subdir is on the other server, but just plain old '/' will not work.

Here is 开发者_运维技巧a copy of my .htaccess

# Helicon ISAPI_Rewrite configuration file
# Version 3.1.0.69

RewriteEngine on
RewriteBase /

RewriteRule (.+) http://internalsite/$1 [P]

<Helicon>
ProxyConnectTimeout 120
</Helicon>

There is no default document in the internalsite, as it uses mod_rewrite (wordpress).

but just plain old '/' will not work

This may be because you have the RewriteBase cutting off the slash and then (.+) doesn't match as you have no more characters. Please try to fix your config like this:

RewriteEngine on
RewriteBase /

RewriteRule (.*) http://internalsite/$1 [P]