jQuery not defined

[aeh]

Registration with a validation error - checkbox not selected, existing email etc - prints

Code:

Notice: Undefined offset: 1 in C:\xampp\htdocs\demo\users\helpers\helpers.php on line 75

above the error. Chrome network tab shows jQuery is loaded (twice in 4.2), and console says

Code:

Uncaught ReferenceError: jQuery is not defined at join.php:98

. I've been using 4.1, but this also happens with a fresh 4.2 install.