Assume that you implement Microsoft Exchange Server 2016 in a Windows Server 2016 computer. When a user signs in the Outlook on the web client (previously known as Outlook Web App) or the Exchange admin center (EAC) for the first time, the user can select a culture language. If the user selects an invalid language that has an LCID value of 4096 such as English (Belgium), the Outlook on the web client or EAC crashes with a "System.Globalization.CultureNotFoundException" error message.
This issue prevents the user from signing in until you change the language setting back to a supported one.
This issue occurs because the newly-added cultures don't have valid LCIDs.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.