I have the exact same problem and same error with Dapper Flight 7 when trying to add a Lexmark z53 from a LiveCD session:
E [07/May/2006:09:00:10 +0000] [cups-driverd] Unable to write "/var/cache/cups/ppds.dat" - Permission denied E [07/May/2006:09:00:23 +0000] CUPS-Add-Modify-Printer: Unauthorized -- cannot write /var/cache/cups/ppds.dat https://launchpad.net/bugs/40795 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs