I had the same problem except with the Asrock E3C226D2I board. Do you happen to have AVG anti-virus program installed? Or some other antivirus software? Disabling "LinkScanner Surf-Sheild" under Web Browsing Protection on AVG fixed half the problem for me. It allowed the console image on the dashboard page to connect. Jviewer also was able to connect after but i'm still having problems with jviewer showing just a black screen. I can send commands through jviewer but screen stays black and shows 0fps.
I kept meaning to follow-up with this thread, thanks for the reminder.
Yes, I do have AVG Anti-virus, and indeed, discovered that I need to disable
both "LinkScanner Surf-Shield"
and "Online Shield" for JViewer to work.
The other part of the "solution" depends on your Java version. The latest version (as of today) is Version 7 Update 51. This has more security features, and by default, doesn't want JViewer to run. So you have to go into the Java Control Panel, and either (1) lower your security level to Medium, or (2) add your IMPI IP address to the Exception Site List.
After doing all these things, my experience was similar to yours: I could tell I was sending commands to the server console via JViewer, but the screen was still blank and saying 0fps. But, I could see the console image updating in response to my commands via the snapshot image on the IMPI Dashboard.
I just kind of sat there thinking, and suddenly it started working! I know that's non-specific, but maybe just sit there and wait 5--10 minutes to see if you get any response.
It's an extremely annoying problem. The IMPI functionality looks to be provided by AMI (the BIOS vendor). If you search the web for "Megarac SP Java", you'll find reports of similar problems with other brands of motherboards. I.e., it appears to me the problem isn't just with ASRock. Hopefully AMI cleans up their program.
AVG likewise needs to fix their software IMO.