defaultProxy enabled="true"
I believe the line you changed previously to get through the proxy was; useDefaultCredentials="true".
Do you have a machine that is running 10.1.1.142 version of the Operations dashboard that still can get through your proxy server?
Have you tried to install the 10.2 version on another system that never had Operations Dashboard installed on it?
To get the ball rolling could you please log a support ticket and provide as much information regarding your environment.