I don't have a hard-and-fast rule, mainly because "issues" are situational. While I don't know that the initial issue (keycard not working) would make me walk away, were it to happen to my keycard I would suggest that the other person grab coffee or a drink on me (as someone else suggested) while I resolved the issue. For me, this is as much about the other person not having to listen to the discussion as it is me not wanting the other person to know my credit card was declined!