This is likely to be a local area network configuration issue for you.
We've had a few users with problematic firewall, proxy server or VPN configurations, in the past.
I'm sorry but it's a bit of hassle to track down the exact problem.
The best way to identify this is to login to the site outside your normal company internet connections (e.g. from home, a cellular connection, etc (one that does not use the VPN or company network).
If you can connect correctly this way - it's likely that the issue is a configuration setting inside your office network/vpn/firewall. In this case ask your IT folk to setup a work around or fix the problem.
Sometimes it's just a mater of bypassing your proxy server for the affected domain or adding us to a whitelist.
Alternatively we are happy to liaise directly with your IT people.
If you're still not able to login outside your company network please let us know.