I am sorry to hear you are experiencing an issue. I would be happy to help! If you could provide me with a little more information I could take a look and see if I can't figure out what is going on.
1. What's the name of the email campaign you are experiencing this issue on?
2. When you say box, are you referring to not being able to open the block where you can add content?
2. Or, when you're in the block, clicking on "Add a Link" does not allow you to create a hyperlink?
A screenshot of what you're seeing would be helpful as well, but not necessary. If you would like you can email us this information at social_support(at)constantcontact(dot)com along with your username and a reference to this post.