Skype for Business will prompt users for Exchange credentials when not connected to the VPN.
When working remotely and not connected to the VPN, Skype for Business may ask the user for credentials.
Even after entering them, if the user is not on the VPN, Skype for Business may continue to notify the user to enter their Exchange credentials. This is because Skype for Business synchronizes the user's calendar to their Skype for Business. To do this, Skype for Business needs the user's Exchange credentials. Even though Skype for Business logs in and functions for instant messages and phone calls as it should, the calendar function will not be synchronized until the Exchange credentials are entered.
How Do I Fix This?
1) Exit Skype completely by either a)right-clicking the icon in your taskbar, or b)using the Skype for Business desktop application. Simply closing the program with the "X" in the upper-right will only minimize the program and not fully exit.
2) Connect to the Cisco AnyConnect VPN. For instructions on how to use the Cisco AnyConnect VPN, please follow the instructions here:
VPN Instructions for Cisco AnyConnect Secure Mobility Client - https://answers.uillinois.edu/extension/99063.
3) Once connected to the Cisco AnyConnect VPN, re-launch Skype for Business. Skype for Business should now automatically log you in. Once logged in, you should notice that the prompt for user credentials is no longer there.
4) You can now disconnect from the VPN.