Error in Adobe Sign for Word add-in when Preview & Send toggle is selected

Hi.

My client is having issue when they are using Adobe Sign for Word add-in on our Terminal Servers. The error is on the Send for Signature when the Preview & Send toggle is selected. The error message is "Sorry, an unexpected error occurred. Please restart application or try again later. If the problem presists, contact customer service." Anyone knows how to fix this issue?

We're using Microsoft Word 2016 Pro Plus runing on Windows Server 2012 R2.

Thank you very much.