I just got NCNS'ed, but the lady emailed me later to explain what happened, which was perfectly reasonable, not that I was worked up about it anyway. So, while I don't have a good story, it did get me to wondering what some of the sillier, overly elaborate, or just total BS NCNS reasons people have been given.
I'd love to hear from the ladies as well as the guys, I'm sure the ladies have heard some whoppers.

His wife found out and now they are getting a divorce.  

If he's really getting divorced it should free him up to see you as often as he wants

Divorced men typically don't have much money.

But this was a date, not a provider date. I did not hear from her until the next day, but then I was
ticked off big. So I sent her a couple of really unkind text messages, then that same day she texts
me and says her phone got wet and wasn't working right, did I get her texts? No! Had to tell her
she might at sometime get some really nasty text messages but so far the wet phone never
delivered them. Moral, don't ever give up!

Really dude? O.o

Well, not at first, but from personal experience, when the alimony is all paid, watch out

That's stupid ... I have seen many who "forgot" or don't shave/trim.

I had never seen a provider before and she sent me through the loops to get verified. All emails were quick, pleasant, and I know she verified me via work.  
The first time she over slept and sent me an email hours later explaining herself
The second time she was getting hair extensions and it ran to long, BTW our scheduled time was 11PM.
Not very elaborate but I was new and took my licks.

have never had a provider NCNS me.. BUT I have gotten to know a couple of providers pretty well and they tell me that they get "I was called into work last minute" a lot. SO I guess that is not technically an NCNS because they email or text moments before they are suppose to be there LOL.. I think that is funny .. in this day and age who get's last minute called into work? AND apparently it is a common excuse .. I always felt like just being honest was the best way to go HAHA !

I'm guessing it depends on your job/industry. I get pulled into con calls unexpectedly all the time. I've only had to cancel once because if it, but I knew it sounded lame when I used it as my reason for canceling.

Anyone who has a job where a company operates 24/7 or 24/7/365 ( mine does) it is not at all uncommon to be called in. Anyone in Maintenance,Facilities,Automation, or IT will see this as a quasi-normal situation. I have bee called in on numerous occasions....think Murphy's Law......but have stayed in touch when this has happened....it happened recently....and every time the lady has been very accommodating and understanding. I have also "made it up" to them with a follow-up appointment as well. So yes, it does happen. Frequently? That is very subjective. My .02.......

or your wife found your stash, I would rather know the truth  than some elaborate made up story that makes me wonder if you are okay or not.

Sometimes saying, "my XYZ (close relative) has relapsed and I need to go pick them up right now", isn't an option.
Or some other equally personal, possibly embarrassing situation has occurred but you need to say something so your not a NCNS. If that is what happened one may feel the need to make up something because a simple "urgent problem must cancel" will not be enough for inquiring minds. So there's something to think about, especially if the person is usually reliable.
          You may just want to be glad you were notified.

This isn't about someone on this board.....

I had TWO outcalls cancel within minutes, which has NEVER happened to me before.  The first one sent an email saying, "off  off" as I was heading out the door!  WTF?  He later wrote a woman cozied up to him at the bar, and guess what happened after that?  She must have been offering herself up for free, because free trumped ME.  

He passed away! Mi you he also owed me a cancelation fee. Then about 2 weeks later I see him on the board.