I have just updated W3TC to the latest version and while everything appears to be running fine, I get an odd error when I test the Cloudfront distribution using the button in the "Configuration" section of the CDN sub-section on the dashboard.
When I test it gives the error "Empty Access Key", despite working fine before and even when I try a different access key and secret key I still have the same problem.
However, when I check files and images on my site I can clearly see that they are being served correctly from the CDN. Perhaps it is the error message at fault as everything else seems to be functioning perfectly.
Anyone else with a similar issue or fix?
(There is a tread for issues with MAXCDN as well:
with some people reporting a similar issue)