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.
@ZOS_GinaBruno Is this going to be fix soon as it a bad bug /also you cant enter delvs in the campaign with this bug.