The 12029 error code means that the EPA plugin could not connect to VPN virtual server. Refer to https://msdn.microsoft.com/en-us/library/windows/desktop/aa385465%28v=vs.85%29.aspx for more information.
This is a network related issue and this kind of issues are mostly caused by firewall or other security related software. To verify, disable firewall and anti-virus, and then try connecting again. If this solves the issue, then add a rule for white listing nsepa.exe (EPA plugin process) and nsload.exe (VPN plugin process)