Got a 412 error

I thinks its a great gallery, exactly what I was looking for.

But when I try to upload images to an album I get this error:

412 Error
Your request got filtered out due to possible security issues.
One or more things in your request were suspicious (defective request header, invalid cookies, bad parameters)
If you think you did nothing wrong:
try again with a different browser
avoid any evil characters inside the request url
If you are the owner of the website, you can consider revising the rules of the mod_security module or turning it off from your Web Hosting Control Panel.

There someone that can help me?
Thanks guys