Hey there @Blackmoon777
The error message "You are already queued for that campaign" seems to occur when a player is disconnected or crashes while queued for a campaign. It is possible to bypass this error by joining the queue as a group, or grouping with another player who is inside the campaign and using the "Travel to player" option.
We know you mentioned travel to, but please try doing this while grouped with a player that is in the campaign as opposed to a guild member. If that doesn't work, try relogging then check your notifications (press the N key by default). If you see a message to join the queue for Thornblade in there, click X to reject it, then try entering the campaign again.