I found the e-mail sending to the user in AJ HYIP not working. Do I have any option to change in admin panel to make it work?
No. first you should double check that e-mails addresses are correct. If so, then the problem could be in your send mail server (or the SMTP server you use) AJ HYIP only makes a call to php mail() function which simply passed the parameters to send mail according to the send mail path file. So the problem could be in your send mail server.