@ John_Pagourtzis You can send me a PM and I will look into it with you or we will use this topic. Can you provide in that PM which Windows versions (32/64bits) and Office versions (32/64bits) you are using. Also please use the latest build provided in Secure Outlook add-in is now available for testing in free-as-in-beer version
Also considering you have tried this on 10 machines so far my guess is that this is a company? Are there any policies in place which might block the add-in or any other for that matter?