This is particularly relevant in your case (an installation error on Aetna's end). One of the biggest problems with health insurance for companies < 1,000 employees is that everything is done via paper / pdf / fax machine. This is of course a pain in the ass, but more importantly it's a source of large and irreducible error. Insurance companies average about 10% to 20% error rates on the stuff that we send them even if Zenefits is 100% correct. These errors aren't unique to Zenefits -- any broker or other company doing this stuff would have them -- and we spend a lot of time following up with carriers to verify, etc....
Here's the important thing -- our growth means we can make insurance companies build APIs for us, some of which are live right now, and many more of which will be live in the coming months. Only with this full electronic integration can these processing errors go away, for us and for everyone else. APIs == zero errors. Existing paper / pdf method can never fully eliminate errors b/c we (zenefits) don't control the guy on Aetna's end who is keying information into their system.
We use Zenefits and (AFAIK) have no issues with the service. Just throwing it out there that a little reassurance goes a long way.
edit: As someone who wants to give Zenefits a serious go but has some concerns.
Are you at liberty (and are willing) to share any specific examples of the problems?