The message that shows that saying that you cannot make or receive calls usually means that the softphone is not able to authenticate to our servers and will not be able to make calls because of that.
But because of the E911 message you are seeing you may not have your E911 address set up in your account. Go to
https://service.ringcentral.com/ and log into your account. Once logged in select the "Settings" tab, select the "Phones and Numbers" tab, then select your phone. On the right-hand side, you will see "Emergency Address", select that and you can enter the address of your home or office where you use the phone.
Once that is entered, if you are still getting the error then you need to look into your network configurations to make sure that the softphone can connect to the RingCental servers.
If you have e911 set up, the address has been entered, Click the checkbox "By clicking I Accept below, you acknowledge and agree that.....". I had some users who did not do this step, an Admin you can do this step for the user also.