Users cannot register

Hey guys,

when people try to sign up at my website they keep on getting the following error message:

Sorry XXX, your request cannot be processed.
For security reasons, it was blocked and logged.

[NinjaFirewall]

If you believe this was an error please contact the
webmaster and enclose the following incident ID:

[ #XXXX ]

Allowing users to register is not blocked so i dont understand where that message is coming from. Looking forward to hearing from you.

H.

The page I need help with: [log in to see the link]