From List Accounts the cPanel button is not working.
I've had this issue before around a time when there was a cPanel update and a reboot fixed it. It's not fixing it this time.
I've gone into Tweak Settings and confirmed that " System>Accounts that can access a cPanel user account:" is set to: "Root, Account-Owner, and cPanel User" (I also changed it to something else and changed it back.)
I've confirmed that root is the owner of all the accounts.
I've modified my pro package and confirmed it is set to have root as the owner and tried to access from a pro account.
I've re-assigned my root password.
Still, after clicking that cpanel button on list accounts, I just get an error message.
What else can I look at?

I've had this issue before around a time when there was a cPanel update and a reboot fixed it. It's not fixing it this time.
I've gone into Tweak Settings and confirmed that " System>Accounts that can access a cPanel user account:" is set to: "Root, Account-Owner, and cPanel User" (I also changed it to something else and changed it back.)
I've confirmed that root is the owner of all the accounts.
I've modified my pro package and confirmed it is set to have root as the owner and tried to access from a pro account.
I've re-assigned my root password.
Still, after clicking that cpanel button on list accounts, I just get an error message.
What else can I look at?
