No, it was not a plumbing issue.  It also wasn't due to a natural disaster or crime.  It was due to VERY high demand.  VERY HIGH!  To the tune of 4,000 burgers an hour.  Here's a tweet from White Castle:

I'll be honest.  I'm not a big fan of White Castle.  But my girlfriend Suzannah totally gets it.  Her first thought was, "lets open 5 more White Castles in Vegas now!"

They have since re-opened.  If you'd like visit the only 24 hour White Castle in Vegas.  You'll find it at the Best Western Plus Casino Royale.  Yep, they kept it classy.