Office 2016: ADD-IN ERROR - This add-in could not be started. Close this dialog to ignore the problem or click "Restart" to try again.

If you receive the mentioned Add-in error in Excel 2016. Please follow the steps given below to resolve the issue .

• In Internet Explorer, click the Tools button, and then click Internet Options.
• Click the Security tab, and then select the Internet Sites Zone.
• Select the Enable Protected Mode check box, and then click OK.
• Restart Internet Explorer and Excel

For more information checkout this article on Microsft Technet.