Dave,
As a start, I would leave all instances of ArchiCAD and then delete the connections.xml file located here:
C:\Users\[username]\AppData\Local\Graphisoft\ConnectionInfo\15.0.0
Then start up ArchiCAD again.
When you changed the password it may have changed permissions to network addresses in a subtle way affecting how applications that use VPN access the DNS server.
Hopefully this is all you need to do.
Ed
Graphisoft Technical Support