Here are the most common reasons for that:
1) You are not logged in.
For data security reasons the overlay is available only for users who have access to the dashboard. Please log in to IO and launch the overlay again.
2) Setting cookies is forbidden in your browser settings. It should be allowed. Please follow these instructions:
3) If #1 and #2 did not help, it can be that IO code was removed or commented on your Home page or the whole website.
Please contact firstname.lastname@example.org for further instructions.