Request failed Site URL not accessible (IP 66.135.55.161 whitelisted)

Hi,

I can't use WP Smush Pro anymore. Anytime I try to smush images I get this error:

Request failed Site URL not accessible

What I already did to try to solve the problem:
- I whitelisted 66.135.55.161 at my MaxCDN account
- I whitelisted 66.135.55.161 at my HTACCESS inside wp-admin to allow access to the folder
- I installed the plugin and logged in with my WPMU DEV Premium credentials

What did I forget to check?

Rick