Outlook Add-in constantly prompting for password for users with PCs connected to wi-fi network

We have an off site building   that only has a wifi network. Every user in that buildinng is getting prompted  by the Outllok add-in to enter their user name and password.  I have not been able to figure it out other than it has somethinh to do with  being connected to the Wi-Fi.  I am at a loss   as to how to solve this problem.  I open to any  ideas you may have.

Thanks,

Rick