Anyone with an answer?
Have you tried showing errors to see if provides any information?:
You can also go to your project page and see if the Add-Ons are listed there:
Roll your mouse over Dashboard--> Click Extend Concrete5-->Scroll down and click the link under "Project Page"--> Scroll down to see your "Add-Ons and Themes," you can also click "Add Add-Ons to your Project" here.
I hope this helps,