Error: unable to unlink ... when using "git gc"

Hello Everyone,

I'm new in git, and when I was practicing the tutorial: http://www.kernel.org/pub/software/scm/git/docs/everyday.html

I've had a problem when using "git gc"

Here is the log:
git@tomato:~/golf$ git gc
Generating pack...
Done counting 121847 objects.
Deltifying 121847 objects...
 100% (121847/121847) done
Writing 121847 objects...
 100% (121847/121847) done
Total 121847 (delta 62587), reused 121184 (delta 62253)
Pack pack-44320b247756067835f5e4a789c7eb5bcc5266c3 created.
error: unable to unlink .git/objects/16/b14f5da9e2fcd6f3f38cc9e584cef2f3c90ebe
error: unable to unlink .git/objects/a1/f6672f6e5bd90acf16a43fea774ca655a3ab1e
error: unable to unlink .git/objects/a8/5cca5b91cf77e8df731827849308ef6dae4536
error: unable to unlink .git/objects/ae/64c9d0ea558e403acf139f690c804212d490be
error: unable to unlink .git/objects/b3/a4c72ea70a3bb43b1819a0a74268870849a21d
error: unable to unlink .git/objects/db/5ec507a2ed86169e4a31bba1d95067c4f3fac4
error: unable to unlink .git/objects/ef/65ed2454b8dcbf8837595d8881ca42898a491c
error: unable to unlink .git/objects/fb/92c37ccc8bdbf3c70bc3afaf8261cedbc92d71
Removing unused objects 100%...
Done.

While I'm looking at these "unable to unlink" files, it seems they are read only: git@tomato:~/golf$ ls -l .git/objects/16/ total 4 -r--r--r-- 1 johnny johnny 26 2009-01-05 09:25 b14f5da9e2fcd6f3f38cc9e584cef2f3c90ebe

Is there anything wrong here?

BTW. I've used git fsck with/without --full, it works fine and no error is reported.

Thanks for your consideration, Johnny