VPN at work and home issue

Hi

I have set up a VPN at my office and all is ok there as I managed to finally get connected to the server PC from my work PC in the same office, at the office I have talk talk broadband now I am at home and trying to connect to the server PC at the office but having issues, I have left the server PC on at the office, we are on sky broadband at home and keeps coming up with error 800, just seeing if anyone could help or point me in the right direction please

Thank you in advance

Ian