I started Basic Beggar's Lightfoot quest, and I didn't feel like my character was really going slow, so I took the shoes off to check and that made me fail the mission. Now when I try to re-accept the mission, the information box at the bottom right of the screen says 'Quest Started', then in red 'Cannot be changed.', then in red again 'Quest Cancelled.' The quest fails before the NPC's dialogue is even over.
Send a ticket. Maybe they can reset the quest for you. Next time just check if you have the shoes on or not. If you have them, don't take them off! xD