I have had a trailer connection error in the past, usually fixed by "jiggling" the trailer plug when plugged into the truck. And/or the error just goes away after a couple minutes of driving. But... the brakes and lights still work, even with the error.
I have read about others with a similar issue, and many times replacing the receiver plug on the truck solves it.
This is completely unscientific, but I think a lot of Ford trailer plugs in the 2005 to maybe 2010 range just had some minor wiring issue.
If it happens again, I suggest just replacing the trucks receiver plug.