403 Forbidden error message after login

Hi

I use Profile Builder. The registration works perfect, there is no trouble. But some of the user have the problem that they can’t log in after the succesful registration. They enter their mail addres and password but it does not work, it always shows:
403 Forbidden You don’t have permission to access / on this server

It’s strange, because I managed to log in with the same credentials on another computer. I tried it with several computers and browers but there is no schema, I mean it’s not a computer problem.

Can anyone help me solve that issue?

Thanks!

https://ww.wp.xz.cn/plugins/profile-builder/