The 2.6 kernel prefers opening the files directly, as I recall.
I also see such a warning when booting Fedora Core 2 test1:
$ dmesg | fgrep quota
quotaon: numerical sysctl 5 6 18 is obsolete.
*** Bug 115886 has been marked as a duplicate of this bug. ***
sorry for the bugspam, adding myself to cc list.
I've testing on RHEL-4 and RHEL3-U4 and have been unable to replicate
this bug. It may have been a temporary problem with the Fedora Core 2
test1 kernel & the kernel the quota package was built with being out