ERROR: Cookies are blocked or not supported by your browser

Sometimes, when you try to log in to your site, you may encounter this error:

ERROR: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.

This is a problem that can be due to many different reasons, and caching can be sometimes responsible for this.

First of all, you should really check that browser supports cookie and they're not being blocked.
If so, the error could be due to the fact that you have custom login page.

WP Rocket does not cache the default WordPress login/logout URLs.

But if you are using custom URLs, WP Rocket won't be aware of them, so you should manually exclude those URLs from the cache, following this tutorial: Exclude pages from the cache.

If you're not using a custom login page, and this solution doesn't help, we suggest you to refer to the many threads you will find on this topic.

See for example: http://wordpress.stackexchange.com/questions/166181/cant-log-in-error-cookies-are-blocked-or-not-supported-by-your-browser-you