I have/had this same sort of issue with version 6 as well. Only my ERA server is on a Windows 2008 machine. All the clients that the remote agent is going to are WIndows 7 based machines. Two things I've noticed - whether they help or not, that'll be up to you:
1. The Windows firewall, if on, will block the install. Turning it off will *sometimes* allow it to install, but will still fail due to #2 below
2. We have a Barracuda Web Filter 610 installed which blocks web access if the user has not authenticated against Active Directory. If the client machine (and possibly the ERA server, I'm still testing this one out) does not have web access, the remote agent won't install. The error generated on the backend ends up being: Failed to synchronize package repository.
More often than not, the firewall is the cause - at least in my experiences with my machines. Not sure if that helps at all, but figured I'd contribute as I've experienced this sort of thing as well.