@tempkimway - I read and understood the original concern, which is why I asked them to send the invitation again to see if the problem happens again or if it was an isolated incident. If we can't accurately reproduce the problem, we're not able to find and fix what might be causing the problem. Since two of the three invitees were able to click the "accept invitation" successfully, it might mean there's something specific on that user's computer that could be causing the issue.
Can you have your friend take a screenshot of the invitation on their computer so I can see what they're seeing? You can upload the image to a image sharing site like https://droplr.com/ or http://getcloudapp.com/, or you can upload the image to your site's media gallery and I can take a look. This page has some helpful tips for taking screenshots:
I hope that clarifies things! Let me know if you have any questions.