Looking again at the logs I have this error, that was causisng VMs on that hypervisor went to RO:

Dec 8 09:53:56 [kern.info] kernel: [978191.413459] iscsi-scst: ***ERROR***: Connection with initiator iqn.1994-05.com.redhat:eba5969b759d unexpectedly closed!

But this is before the I/O error at:

2011/12/08 09:56:15|I/O Errors detected on unit S004. The unit requires your urgent attention in order to decrease the risk of data loss.

Is the same error? second one was reported later but is the root of the first one?

Regards
Carlos Luna