If a disk has erratic blocks, it will loose first DMA, then tries PIO, and at last reset the bus. I had to recover failing harddisk several times for customers, this one looks a bit different, as I always had IDE opcodes and reset messages in log. The freezing system is a sign for kernel trouble.
Sometimes now I see the last message in the log is ide0: reset: success then then machine freezes. But it does not occur every time. I have stripped down the machine, disconnected and reconnected the hard drives. I have re-installed LINUX (though not yet allowed YOU to get any updates) using the same LVM disk partition arrangement, but re-formatted all the partitions. I am presently restoring the data to the LVM. I will let you know if the problem recurs. If this still fails then I will switch to an alternative mobo ie change the ide controller chip.. before finally sending the Primary Slave disk back to the supplier (it is only 10 months old). Thanks for all your ideas. Philip