I am running into this issues, few VMWare VM's that are running with RHEL 5.6 and Centos 5.7, are having read write errors on the root file system. This is noticed on all vm's. After looking to log files this what I noticed.
touch: cannot touch `test.txt': Read-only file system.
after this we have reboot the server, during booting up, fsck is fixing the issue, in one case we had to rebuild whole VM as did keep on panic, it did'nt as prompt for fsck.
some of the log message error that I noticed.
Jan 18 13:25:01 Hostname1 kernel: EXT3-fs warning (device dm-0): ext3_clear_journal_err: Filesystem error recorded from previous mount: IO failure
Jan 18 13:25:01 Hostname1 kernel: EXT3-fs warning (device dm-0): ext3_clear_journal_err: Marking fs in need of filesystem check.