When doing Trader Quests you shouldn't be able to use most forms of travel including:
https://uo.com/wiki/ultima-online-wiki/gameplay/quests/trader-quests/
"Read his offer carefully, there are problems in accepting this commission. You may not recall, gate or sacred journey, even Skara Ferry and the teleport tiles in Jhelom and Moonglow can’t be used, so be sure to take with you a boat to enable you to cross the seas. You can use the public moongates, but to do so will forfeit any distance bonus and rare chance at rewards. Taking a short-cut through the Solen Nest is also not possible. "
You can currently use Crystal Portals, Corrupted Crystal Portals, and other player's moongates to get to your destination.
https://uo.com/wiki/ultima-online-wiki/gameplay/quests/trader-quests/
"Read his offer carefully, there are problems in accepting this commission. You may not recall, gate or sacred journey, even Skara Ferry and the teleport tiles in Jhelom and Moonglow can’t be used, so be sure to take with you a boat to enable you to cross the seas. You can use the public moongates, but to do so will forfeit any distance bonus and rare chance at rewards. Taking a short-cut through the Solen Nest is also not possible. "
You can currently use Crystal Portals, Corrupted Crystal Portals, and other player's moongates to get to your destination.