Usb not a valid block device

["牛坤" <haoniukun@sohu.com>]

Dear debianers,

I've a Debian3.0 r2 installed.
I updated my kernel to 2.4.18.
Each time I want to mount my usb mass storage device.
mount -t vfat /dev/sda1 /mnt/usb
I always get the error code "not a valid block device".
Read from some maillist that I should install the sd_mod module.
Once again, I compiled the kernel again.
I can see the sd_mod.o file.
But still I can't load the module.
Would someone be kind enough to give some hints?

Thanks in advance.

Sincerely,
Kun