What does “Unkown link error occurred” mean?

This is a bug in TradeStation.

To resolve, please exit TradeStation and the TradeStation Development Environment.  Run my KillTS utility to remove all stray TradeStation processes from memory, or you can simply reboot your computer.

Then, start the TradeStation Development Environment (TDE).

Perform a “Verify All” using the following TDE menu option:

For more information, see: https://community.tradestation.com/Discussions/Topic.aspx?Topic_ID=166206