I am writing a simple program to send an email to myself by means of the Microsoft Web Exchange Service. The email uses the WES extended property definition for a voting button type. The email is successfully received by my Outlook 2013. But when I open it, it shows the pop-up window with message "Could not install the custom actions" and the OK button. There is no other message telling me why or what custom actions. When I click the OK button, the message opens with the voting buttons and I can vote (e.g. approve/reject) and send the email. So it actually works as expected.
The only question/problem I have is why it shows the pop-up window, and how can I resolve or get around this?
I have a demo coming up soon that relies on this feature. So any help would be much appreciated.