Contact Form 7: digit module

I’m currently in the progress to migrate our current website (www.smashforfun.be) to WordPress.
Because it will be used primarly as CMS, I’m using a lot of plugins and one of them is Contact Form 7.

A great plugin to rapidly create a form on your website/Wordpress but… I was lacking one functionality. Numeric validation.
Because Contact Form 7 uses modules it was fairly easy to create a module (right-click and Save as) myself.

The only thing you need to do is add a error message in includes/functions.php (in the folder of Contact Form 7).
And that should do the trick… well… there was a problem when I added a new element to the messages array. My WordPress didn’t work anymore. When I add a new element something terrible happens I guess

For now, I just replaced an existing error message (which I don’t use right now) but if someone knows what causing this issue… please do tell!