Hi, I just received my MJ last Saturday and set it up Last night withing half an hour. I, too, had the Error 400 when I clicked on my MJ icon to kick it off and register. I must say that it could be confusing even for an IT person like me since the documentation (or lack thereof) that came in the packaged is very MINIMAL! Any way, after working tithe the Technical Support chat person, I SUCCESSFULLY registered my MJ and all is working fine now.
In short, in my case, the cause of my Error 400 was due to my Norton Internet Security Firewall. So, when you register your MJ (to use it for the 1st time:
1) DISABLE YOUR FIREWALL!
2) double-click on the magicJack error 400 message ( displayed in the "greenish" box in the middle of the MJ soft phone panel.
3) the Registration Log-in screen will pop up: re-enter your correct email address and password and click on the "Next" button.
4) It should take a few seconds and now where it used to display the Error 400 message, it should now read "Ready to Call" and then your new MJ phone number is displayed below it.
I hope this hepls. Good luck to all! I know it could be frustrating sometimes, but technology will do that to you sometimes!
