On the back of the Arris, I believe there should be a tiny reset button. Take a paper clip and hold down that reset button for at least 15 seconds (when is doubt hold it down longer). This will hard reset the modem. Hopefully this will get whatever bizarre problem cleared out and get you going so your changes stick. If this still doesn't work, contact WOW_Dan, he can probably get it bridged for you remotely.
As a side note, there are many posts on this message board about people with problems with your particular modem. If you actually own your own modem, and you have a internet tier that is 15 Mbps or less (and doesn't require DOCSIS 3.0), you may want to think about using it (and saving yourself the $5 per month).
reply to bdwyzr
Errors like that are typically browser related with these modems. Try using a different browser (Internet Explorer/Firefox/Chrome) and see if it works. If it still doesn't work, shoot me your account number or phone number on the account and I can remotely flip it to bridged mode.