When calls were failing, were you registered, or did you have the Not Registered message?
Indeed, we're on the same page here. When the calls were failing I WAS registered.

the Network Preferences option. If you click on the Features tab in the light blue, then click on the Preferences word in the dark blue bar, the choices on dark blue menu bar change. You should see the option for Network Preferences after you click the Features tab, then the word Preferences.
For me, features > preferences > yields:
Advanced Display PIN Softphone / BYOD Password

No network tab.

I don't think I asked--do you have a number entered in the 'failover' feature, or do you failover to voicemail
Failover to voicemail.

Another thing I've noticed and commented upon is that VPanel does not seem to be consistently implemented for IE8.
I've tried it with IE8 and Google Chrome and get the samething.