I have tried it for many times. but the error was yet the same. My domain is 'jisubar.com'. Since now, I can neither set it as the main domain nor add it to the domain list with Cpanel.
I tried to modify main domain as my own one, but it ended up with an error message below:
Hosting Domain Modification
submitted: July 1 at 2:06 am
code: RCIVIZ6PLMR
Saction status: Error
information: A change to your hosting account's primary domain.
result: A system error occurred while...