The 775 error message is an indication that the DirecTV receiver is not seeing a signal. The Trav'lers faceplate appears to indicate that the system is locked onto the correct satellites.
It appears that this particular error is often caused by a bad piece of coax. Is this a new Trav'ler? Have you been able to use it before this?
The wiring isn't all that difficult--
From the DirecTV receiver to the power injector, from the power injector to the Trav'ler. Do you have the correct port of the power inserter connected to the receiver? That's the one place you could make a mistake.
Joel (AKA docj)--
RV Technology Specialist