Question about HD / UDMA capability

Hi,

I just tried to set my HD to UDMA 5 but it gives me a read/write IO error.

Model: IBM Travelstar IC25N030ATCS04-0

bash-3.00# hdparm -i /dev/hda

/dev/hda:

Model=IC25N030ATCS04-0, FwRev=CA3OA71A, SerialNo=CSH305DAGLYTVB
Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
BuffType=DualPortCache, BuffSize=1768kB, MaxMultSect=16, MultSect=16
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=58605120
IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 *udma2 udma3 udma4 udma5
AdvancedPM=yes: mode=0x80 (128) WriteCache=enabled
Drive conforms to: ATA/ATAPI-5 T13 1321D revision 3:

* signifies the current active mode

bash-3.00#

bash-3.00# hdparm -X udma5 /dev/hda

/dev/hda:
setting xfermode to 69 (UltraDMA mode5)
HDIO_DRIVE_CMD(setxfermode) failed: Input/output error
bash-3.00#

What could cause this?
I'm very new to Linux and don't want to ruin anything.

Thanks for looking!

Marinus.