I just got the loansome road DLC. I went to the start of the mission in the canon with the debris door but when I try to enter all I get is a message that states "you cannot bring others with you... ". It doesn't say who or how I get rid of these others. Is this a bug or have it just been too long since I played Fallout and I have forgotten some companion setting?

Goto the gun runners and use the companion dismissal terminal. ^_^

Go to gun runners or lucky 38 and dismiss companions with the terminal you should be good then

Thanks, that did it. I had a faint memory that I had a dog as a companion long ago and sure enough.
Bethesda should remember that it can be quite a while between someone completing the game and the getting a DLC so s refresher would be good to have. Like that there are only a few places where you can get rid of your companions and you have no indication that you have one.

Actually, current companions show up as a marker on your pip-boys world map. But yeah, I guess you could easily forget having a robotic dog.