Skype for Business, IP Phone Error, Cannot download certificate because domain is not accessible
If you receive the error "Cannot download certificate because domain is not accessible. If the problem continues, contact your support team." while attempting to log in to an IP phone that is “tethered” by a USB cable to your computer, the following workaround will allow you to successfully log in.
Using PIN Authentication to sign in to your IP Phone after receiving a certificate error
- Unplug the USB connection from the back of the IP phone.
- Unplug the phone’s power source.
- While the phone is powered off, press and hold both the * key and the # key on the phone simultaneously while plugging the phone’s power source. (If the phone still has problems downloading the certificates after completing all the steps in this article, follow these instructions again, but holding down the 4 and 6 keys to perform a complete factory reset.)
- When asked, choose “Yes” to erase all user data. The phone will reboot.
- When the phone reboots you will be asked to select a language for the phone. English is selected by default.
- When asked if you will use a computer to complete the setup process, choose “No”.
- When asked, enter your 7-digit phone number (e.g. 3330000).
- When asked enter your UC PIN. If you don’t know your UC PIN, you can reset it here: https://dialin.uillinois.edu/.
- When asked, enter a new screen lock PIN. The screen lock PIN is used only to unlock the phone after it has been inactive for a period of time. The screen lock PIN is only stored on the phone and has a different purpose than your UC PIN, though you can set both PINs to be the same. Press the “Next” button on your phone.
- Enter your screen lock PIN a second time to confirm you entered it correctly. Press the “Done” button on your phone.
- The phone should successfully sign in to Skype for Business. If not, repeat the steps above or contact your IT Professional or the Technology Services Help Desk.
- Reconnect the USB cable to the phone and ensure that you are signed in to Skype for Business on the computer that is connected to the phone by the USB cable.
- On the phone, press the Menu button and select “Switch User".
- When asked, press “Yes” to confirm that you want to sign out the current user and sign in a different user.
- When asked if you will use a computer to complete the setup process, choose “Yes”.
- On your computer you should be prompted to enter your Skype for Business username and password to sign in to your phone.
- Once you are successfully signed in to your phone, the phone will download the root/issuing certificate from the Skype for Business server and cache the user's authenticated certificate. This should allow you to reboot your phone without receiving the certificate error for at least 30 days.