iFrame Flow shows in Preview Mode Only

Looks to me like you are testing it in the context of a community (That very generic error message is typical for a community - and frustrating).  You should explore the specific URL that is getting passed into the Skuid page to show the Flow (probably in an iFrame)  I’m suspicous that a community prefix is not getting included.  You’ll remedy that in  your iFrame code.  You can use the {{$Site.Prefix}} global merge function to populate the correct prefix for the community at hand.  More information here: 
http://help.skuidify.com/m/11720/l/187263-global-merge-variables-functions