I cannot believe that you spill the beans:
"The value of “ROC 1” is too small, a minimum value of 11 is required."

Please do not reveal this!

Reproduce by just hitting ENTER upon registration:
The username you entered is too short.
The password you entered is too short.
The password confirmation you entered is too short.
The e-mail address you entered is too short.
The e-mail address confirmation you entered is too short.
The confirmation code you entered was incorrect.
The value of “ROC 1” is too small, a minimum value of 11 is required.

https://www.phpbb.com/kb/article/custom-profile-fields-as-an-anti-spammer-tool/