Orange Border message

Hi there,
Did not find any solution on how to fix this issue.
I used Contact Form 7 on dozens of websites but never got that.

I get the message : “There was an error trying to send your message. Please try again later.”
with an orange border, it apparently means it’s spam but don’t know how to fix it. I installed W3 Cache to see if it would fix it as the FAQ says it can be a cache problem. but nothing changed.

The weird thing is that it used to work before.

Any ideas ?