If the Slate 7 is connected to the corporate network, chances are the corporate proxy is configured for all internet traffic which would include traffic from the Slate 7.
The iptables prerouting table or similar (I believe the firewall has changed) will need to be configured to redirect ports 80 & 443 to the proxy’s port.
I’d check with your networking & security teams beforehand. It sounds like you are trying to bypass a corporate proxy which is there for security reasons. Probably state with what you are trying to achieve as there may be alternative solutions which fits the security model.