SOLUTION:
We have made some adjustments and are now seeing users are able to download again. Please close and reopen the launcher to try again. If the issue is still occurring for you, please let us know by updating your post.
UPDATE 6/26/14
Because the widespread issue has been resolved, we are closing this post and locking additional comments.
If you are experiencing an issue with the Subscribe button, please view this post and take the steps provided there:
If your issue persists, please make a new post, and we will provide assistance
Thanks