I've been using Online Armor free for a while and installed it on numerious PCs with no problems. I installed in on a new PC the other day, but I can't get passed the "Invalid Server response. Please try again in a few minutes or contact support" error.
I've had the error in the past, due to OA disconecting my 3G dongle just when the option to choose appears - then me selecting while there's no connection etc. Either that, or a poor net connection with the 3G. This time though, I just can't get passed this section to install. My connection is fine, I can access google from Firefox etc.
I installed Zone Alarm temporarily, but I'm not keen on it.
Are your servers working still?
Edit: I'm adding some details to help...
Clean install of Windows 7 with SP1
Windows Security Essentials
MS updates off tempoarily
Core-i7, 16GB RAM etc.
I have installed as I said, Zone Alarm, but have tested also with and without, plus turning it and giving Online Armor open connections.