You may need to make a custom initrd file with the driver you compiled set
to preload.
I'm not sure what your driver module is called, but here is a basic example
of how you would do so:
mkinitrd --preload=<driver> /boot/<image name> <kernel version>
This will make sure that the driver is loaded before the kernel tries to
mount your filesystem. I have had to do this in the passed with my promise
sata raid controller in my laptop, as well as several of the usb related
drivers to boot off a USB disc. Otherwise the error is the same as what you
are getting.
Don't forget to make sure the initrd line for your kernel in grub.conf
matches <image name>.
