kernel 2.6.8-1-686-smp (2.6.8.4) not boot on HT system

["Norberto Altalef" <nalt@ub.edu.ar>]

I was running kernel 2.6.8-1-686-smp (2.6.8.3) in a Intel D865 PERL
motherboard with a P4 3 GHZ HT processor without problems.

When I upgrade to 2.6.8-1-686-smp (2.6.8.4) the box freeze during boot,
every time after the message ACPI Revision 20040326.
Sometimes display the message "Unable to handle kernel NULL"  and
sometimes nothing. The only way is the reset button.

I can boot if HT is disabled in the bios.

After some search, I probe passing acpi=ht parameter to the kernel in my
lilo configuration. That solve the problem .

As far I know ACPI is related with power saving and I'd would like to know
how is related with this problem.
I would like to know what is the meaning of this option and in adition if
I'm loosing some funcionality.
Is there any change in the new version in the ACPI area ?.

In short I have my problem solved, but I don know why.

Any help or comment would be useful.

Thanks in advance

Norberto