This error seems to happen only in some specific cases as it's the first 
time I've seen it even though I've booted the same kernel before without 
the problem.

WARNING: at fs/sysfs/dir.c:463 sysfs_add_one+0x35/0x3d()
sysfs: duplicate filename 'vcs1' can not be created
[...]
WARNING: at fs/sysfs/dir.c:463 sysfs_add_one+0x35/0x3d()
sysfs: duplicate filename 'vcsa1' can not be created

Same issue has also been reported for Ubuntu with their 2.6.24 kernel:
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/196409
and is also mentioned in this tread for 2.6.24-rc7-rt2:
   http://fixunix.com/kernel/328116-2-6-24-rc7-rt2.html

Cheers,
FJP