Issue with registration form on iPad

Hi there,

We’ve had a few people here and there say that they get an invalid username error that pops up on the registration form (http://simplyjesusgathering.com/join/register), and I had this support request come through regarding someone who was having the issue on her iPad:

No matter what username she puts in, it says “username invalid.” The red message popped up as soon as she started typing. So, I tried it from my computer (mac), and all the ones that were rejected on her iPad, worked. So, I tried on my iPhone, and they all worked as well.

Do you know what would cause that issue?