I don't use MyHours but I can tell you that there are only a certain number of simultaneous connections allowed to any MySQL database at a time. So, if they have 250 connections then the 251st one will be denied but it doesn't necessarily mean the data is lost - it's all sitting there but there are too many people on the site.
They're probably just getting too big for their britches
It could also be that they just have a syntax error in their code but that doesn't seem as likely as being just plain busy.
Either way, I wouldn't worry.
I was curious about who owns this site - in case anyone else is too,
here's the info