zsh: Input/output error: /bin/su

I was trying to login on a remote machine using ssh. Here is what I was getting:

$ ssh nas
Linux dhcp-67-184 2.6.32-bpo.3-amd64 #1 SMP Mon Mar 15 13:49:35 UTC 2010 x86_64

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
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Last login: Mon Aug 16 16:43:07 2010 from dhcp-67-216.isc.ens-lyon.fr
/usr/bin/X11/xauth: error in locking authority file /home/mpiuser/.Xauthority

$ ls
/bin/ls: cannot access 2: Permission denied
/bin/ls: cannot access l1: Permission denied

$ /bin/su
zsh: Input/output error: /bin/su

After a reboot it looked like reiserfs was lost

[ 27.720130] i801_smbus 0000:00:1f.3: PCI INT C -> GSI 20 (level, low) -> IRQ 20
[ 401.812703] REISERFS (device dm-1): Removing [208 28805 0x0 SD]..done
[ 401.812794] REISERFS (device dm-1): Removing [208 28720 0x0 SD]..done
[ 401.812840] REISERFS (device dm-1): Removing [208 28666 0x0 SD]..done
[ 401.830679] REISERFS (device dm-1): Removing [4 25190 0x0 SD]..done
[ 401.851085] REISERFS (device dm-1): Removing [147 12708 0x0 SD]..done
[ 401.851348] REISERFS (device dm-1): Removing [3999 10729 0x0 SD]..done
[ 401.870350] REISERFS (device dm-1): Removing [163 10652 0x0 SD]..done
[ 401.870437] REISERFS (device dm-1): Removing [163 10651 0x0 SD]..done
[ 401.870487] REISERFS (device dm-1): Removing [163 10649 0x0 SD]..done
[ 401.893311] REISERFS (device dm-1): Removing [163 10647 0x0 SD]..done
[ 401.893442] REISERFS (device dm-1): Removing [163 10645 0x0 SD]..done
[ 401.893485] REISERFS (device dm-1): Removing [163 10644 0x0 SD]..done
[ 401.894101] REISERFS (device dm-1): Removing [163 10643 0x0 SD]..done
[ 401.894360] REISERFS (device dm-1): Removing [163 10642 0x0 SD]..done
[ 401.894399] REISERFS (device dm-1): Removing [163 10639 0x0 SD]..done
[ 401.894441] REISERFS (device dm-1): Removing [163 10634 0x0 SD]..done
[ 401.894486] REISERFS (device dm-1): Removing [163 10633 0x0 SD]..done
[ 401.894527] REISERFS (device dm-1): Removing [163 10630 0x0 SD]..done
[ 401.894569] REISERFS (device dm-1): Removing [163 10627 0x0 SD]..done
[ 401.894619] REISERFS (device dm-1): There were 19 uncompleted unlinks/truncates. Completed
[ 402.415653] loop: module loaded