If the customer pastes that URL into the browser he can access the product listing .xml file.
Environment
SIM 7
Proxy Server
Cause
Customer was using an incorrect user name for the proxy settings when requested by the SIM installer.
Resolution
The customer was using "domain\user name" in the "User Name" field in the proxy configuration page.
Had to delete the domain and only use the "user name" and the SIM installer could then access the product download .xml file and finish installing.