I received the error 0x800704D4 today when trying to help a client with their SSTP VPN issues.
While there are many causes for this error to occur this was not one of the issues I found listed so I thought I would share it as an option.
This was caused because there were not enough SSTP VPN ports free in routing and remote access.
On the server (in this case SBS 2008)
Start – > Administration Tools -> Routing and remote access.
Click the + to open the site -> Right click on Ports and select properties
Highlight the Wan Miniport (SSTP) option and click Configure at the bottom -> Add the number of ports you require and click Ok.
Now try connecting the SSTP VPN connection again remotely and hopefully your issue will be resolved.