The first thing the Welcome Wizard does is check to see if it can connect to the Internet. It uses the settings configured in Windows Control Panel > Internet Options for this.
Please check that the connection settings are correct (Control Panel > Internet Options > Connections Tab), particularly any Proxy server settings under the LAN Settings button.
Flexor will use Proxy server settings if they are configured but does not currently support proxy servers that require passwords. Advanced Proxy settings in Windows Internet Options does however allow entering of exceptions. If required please enter:
betaxmpp.camrivox.com, alphaxmpp.camrivox.com & deltaxmpp.camrivox.com