Is this happening with all of your iPhones or just some?
You can usually ignore the second event, that is normal and there will be tons of them. They just mean that for some reason or another the device is failing it's check in and it will continue to try until it succeeds. Unless you see this error consistantly for the same devices and never successfully checking in, then you want to figure out why it's failing.
I have no experience with the enrollment agent (will be setting ours up any day here) but I'll try to help where I can.
Thanks for your help.
I have reinstalled EMM and now it works fine.
Without Enrollment agent...
That's to bad.. I will be installing the enrollment agent in the next few weeks. I hope I have better luck with it.