Pretty sure this error is due to the target grid not being able to verify your DNS/IP address correctly. Can be commonly caused if your self hosting on your LAN from behind your home internet/broadban...
I set one up using my Digital Ocean droplet, basically with an IP address on the internet, opened up all necessary ports using ufw, and I still get the issue. TPing to a wide range of other grids work...
There is information on how to configure to use Hypergrid mode rather than standalone on the OpenSim wiki at http://opensimulator.org/wiki/Configuration
Also some information relavent to OSGrid (al...