Can't access OpenVPN server from behind a proxy

[josejorge]

I have set up an OpenVPN server in my home. I can access it from other devices from several locations: my Android phone, my laptop running Ubuntu, etc. However, I can't reach it from a location where the network is using a Squid proxy. I have a static IP and the Squid machine assigned as proxy, when trying to access my OpenVPN server at home I receive these messages:

TCP/UDP: Preserving recently used remote address: [AF_INET]xxx.xxx.xxx.xxx:xxxx
UDP link local: (not bound)
UDP link remote: [AF_INET]xxx.xxx.xxx.xxx:xxxx
TLS Error: TLS key negotiation failed to occur within 60 seconds (check your network connectivity)
TLS Error: TLS handshake failed
SIGUSR1[soft,tls-error] received, process restarting

Any idea of what could be the problem?