Did you examine the file /var/log/cups/access_log ? Your last post indicated that cups-pdf_log is empty, but what about /var/log/cups/access_log ?
Your error_log shows ten errors, all logged at the beginning of the file. The last error indicates "Scheduler shutting down due to program error," which seems fairly damning, almost certainly related to your printing problem.
The error just before the scheduler shut down indicates that a PAM authentication error occurred. This was likely the reason the scheduler shut down.
The eight errors preceding the PAM authentication error indicate that CUPS did not recognize the four directives listed below, but the error log does not indicate the values that the server encountered:
JobPrivateAccess on line 122 of /etc/cups/cupsd.conf.
JobPrivateValues on line 123 of /etc/cups/cupsd.conf.
SubscriptionPrivateAccess on line 124 of /etc/cups/cupsd.conf.
SubscriptionPrivateValues on line 125 of /etc/cups/cupsd.conf.
In my cupsd.conf file, each of these directives appears four times in the file, and each time they appear they only have the parameter "default" following the directive, like so:
JobPrivateAccess default
JobPrivateValues default
SubscriptionPrivateAccess default
SubscriptionPrivateValues default
Could you please open your /etc/cups/cupsd.conf file and search for these four directives, and tell us how many times each directive appears, and what parameter follows each directive?
If your /etc/cups/cupsd.conf shows parameters other than "default" for these directives, you could try saving a backup copy of your existing /etc/cups/cupsd.conf file, then editing the file to set the parameter following each of the four directives to "default". Be sure that the edited file retains the same permissions and access as the original file, then reboot your machine and see whether you can print.
Also, in one your previous posts, I notice that your Brother printer is not set as your default printer. You might try launching the Printers dialog from the Control Center, and setting your Brother printer to be the default by right clicking on the printer's icon and selecting "Set as default" on the context menu that pops up.