I've just reproduced this thanks to another bug report. Reopening.
The error message is one of:
The username you entered is invalid. Note that usernames must start with a lower-case letter, which can be followed by any combination of numbers and more lower-case letters.
or:
The username you entered (${USERNAME}) is reserved for use by the system. Please select a different one.
I've just reproduced this thanks to another bug report. Reopening.
The error message is one of:
The username you entered is invalid. Note that usernames must start with a lower-case letter, which can be followed by any combination of numbers and more lower-case letters.
or:
The username you entered (${USERNAME}) is reserved for use by the system. Please select a different one.