deleting a file

[Soo-Hyun Choi]

accidentally, i have changed a file permission to 600 with root
privilege. since then, i cannot delete this file.

[code]

[soohyunc at server-01 /] $ sudo rm -f thisfile.a
[sudo] password for soohyunc:
rm: cannot remove `thisfile.a': Operation not permitted

[/code]

is there any way to delete this file from the system?
(i'm using gutsy 7.10)

thanks,