VERIFIED SOLUTION i
When the Content Author client attempts to create a message, a pop-up window "User Account Control - Do you want to allow the following program to make changes to this computer?" appears, prompting for a Windows login.
User Account Control (UAC) is a technology and security infrastructure introduced with Microsoft's Windows. It aims to improve the security of Microsoft Windows. A user account may have administrator privileges assigned to it, but applications that the user runs do not inherit those privileges unless they are approved beforehand or the user explicitly authorizes it, limiting application software to standard user privileges until an administrator authorizes an increase or elevation.
ResolutionUPDATED: April 12, 2017
An administrator must log in to satisfy the UAC requirements. Thereafter, the Content Author client should be able to enter messages without intervention.