Hi Fabio,
Thanks for reaching out with your BoldGrid Post and Page Builder questions!
Can you tell us exactly what you’re experiencing as a result of this message? The message here doesn’t look to be an official error, but instead a Warning message. Normally these messages do not effect the functionality of your website.
If you could let us know your WordPress version and PHP version we can test this on our end to see if we receive a similar warning and if so, take the steps to resolve it.