simultanious login on different laptops with same user

Hi,

I have a small website for a school where teachers can submit the result of their students. I make them login a user ‘teacher’ and they get redirected to the a contact 7 form for submitting the points.
They ofter encounter problems, but so far I haven’t been able to repeat the problem myself.

I was wondering if there could be a problem when different people from different laptops try to login with the same username? Is there a maximum?

Regards,
Remco