Error when entering new user

[wimfeijen]

When I create a new (admin) user and fill in all required fields, the form gives an error:
"A Nickname is required. Please choose a nickname or fill out your first and last name."

Three things seem wrong:

1. I am using a Dutch WordPress installation, and the error message is in English.
2. I filled in all required fields
3. The form has no nickname field.

Filling in a first name and last name helps though. :]

Using WordPress 4.1, Dutch version

[SergeyBiryukov]

That message comes from the iThemes Security plugin, not from WordPress core.