We set up a site with a url like www.mysite.com the site is being served by a proxy to come up as
www.theirsite.com/mysite/
We set $base_url to www.theirsite/mysite
This is working correctly to load all the assets on the page but does not work on the admin.
The admin login and all pages on the admin try to post to the root of www.theirsite.com so for instance the /user page tries to post to www.theirsite.com/user this is obviously not working.
We tried clearing the cache on drupal to rebuild all urls as was recommended on many sites, but did not have any effect.
We are hosting our site via iis7 on windows. The version of Drupal is 7.2
What can be done to fix the admin form urls?