Remote access of Xen server

[sparker]

I am just setting up VMs on Xen Server which is going well except that suddenly I cannot access the servers from home using Xen Center. I am using a VPN to connect to the network and once connected can ping the server and can RDP into the actual VMs themselves but I cannot get Xen Center to connect. It will connect if I RDP into another box and then run Xen center or if I am physically in the school. Weird thing is it used to work and then after the last time the builders turned off the power it stopped. I am wondering if the LA has closed down a port 6936 or something but don't have the wit to know how to check:confused:

Any (polite) suggestions gratefully received!