VPN server

office have  a win2003 which setup a VPN function for our staff...

but one of the staff which in Philippines, always cannot to our VPN.

He using Win8.1,sometime ok,sometime not ok

I have teamviewer to him, and try telnet to our VPN port,it work.

But whatever I try other PC/XP/Win7/win10,it working.

any idea? it always said VPN err 806, i checked web,it said firewall blocked...but if I can telnet, is it mean no any problem? or Philippines ISP problem block?
By the way, user toldl me last week is ok, but today not ok.

** My vpn server using over 2 years already for most of the  China users and no problem.