ISA 2006 - HTTP does not work over IPSec tunnel. All other protocols are fine.

I have a Site-to-Site VPN connecting over IPSec.   Everything works fine across this VPN except HTTP.  

I have read that this is due to the Web Proxy Filter:

http://support.microsoft.com/default.aspx?scid=kb;en-us;885351

There are multiple sources suggesting this, and the advice seems to be to create a new HTTP protocol and remove the Web Proxy Filter from it.  I have done this and assigned it to the policy rule connecting the two sites, but it makes no difference.

Any ideas would be greatly appreciated.

thanks,