Trouble running Custom kernel

I compiled a custom kernel on a virtual box and wen i try to boot the kernel , It says "udev:Wating for device /dev/sda1"and then after 10 seconds it drops to ramfs shell . I think this is a configuration mistake . I tried to make the kernel with the distro specific .config file from /proc/config.gz , But it still doesn't respond . Anybody had this problem before ? May be you guys could help me out .