6.1 installation problem on a big disk

[crschmidt]

I am installing 6.1-RELEASE on i386 platform, using a fairly big IDE disk
(Maxtor 6L250R0, 250 GB).

All goes well when I create a slice and partition it (using defaults). 
I  have
2 disks, ad0 and ad2, but I am using only ad0 for installation.

When the installation begins, I see the following error message:
"Error mounting /mnt/dev/ad0s1f on /mnt/usr : Invalid argument"
and after that the installation give lots of disk writing errors.

ad0s1f is the biggest partition (around 230 GB).

It looks like the motherboard recognizes the disk correctly (it gives the
right size in BIOS Setup). For the record, the motherboard is ASRock 
K7VT4A Pro,
the disk is the IDE Primary Master.

Can I do anything to fix this?

Regards,

Cyril