"du: /u: cannot stat, No such file or directory" problem

[pgd at bbt.se]

I have a funny problem. "du" gives the error "No such file or
directory", on a number of directories in root.

When I run du on my root directory I get:

<<<A lot of files>>>
du: /u: cannot stat, No such file or directory
du: /X: cannot stat, No such file or directory
du: /a: cannot stat, No such file or directory
du: /xenix: cannot stat, No such file or directory
du: /u: cannot stat, No such file or directory

If i do a "ls -l /" from root I get:

(listing is pruned)

drwx------   7 pgd      root         304 Jan  8 18:34 X
drwx------   2 root     root          32 Jul 23 12:29 a
drwxr-xr-x   2 bin      bin         2352 Jan  2 08:33 bin
drwxr-xr-x   9 bin      bin         7472 Sep 14 17:04 dev
drwxr-xr-x   6 bin      bin         1840 Jan 10 11:25 etc
drwxr-xr-x   3 bin      bin         1552 Jul 23 11:49 lib
drwx------   2 bin      bin         1024 Jan  7 14:18 lost+found
drwxrwxrwx   3 bin      bin         3584 Jan 10 11:25 tmp
drwxrwxr-x  11 bin      pgd          224 Dec 19 16:18 u
drwxr-xr-x  28 bin      bin          480 Nov 24 14:47 usr
drwxrwxr-x   4 pgd      root         720 Dec 31 20:10 x
-rwxr--r--   1 root     root      419136 Sep 12 20:21 xenix

Does anyone have an explanation on how I can fix the problem.
tar etc. just silently ignore all those directories, unless they
are specified separately.
Otherwise everything works normally.

P.Garbha