Connecting to sqlExpress over VPN

Also, you would need to make sure that connections can make their way through all firewalls between the client and server.

The fact that you can connect to SQL Express from any machine on the network suggests that the browser service is working.

There was a case apparently similar to this one here, wherein the cause of the problem was a firewall setting on the client computer.  In this case, after VPN was enabled, some additional network rules were applied to the client firewall, which threw things out of whack.

You could try turning off firewalls at server, router and client level and seeing if it works.  Then, switch them back on again, one at a time, to find the blockage.  

Apparently, this is something people came up against with SBS2003 as well, and the typically accepted workaround was to use a Remote Desktop session to access SQL.

 

Thanks to Hyperlink for input on this article.