problem of partitioning

hello,all.after i create a new logical partition using fdisk or cfdisk and exit with "w",there always comes report saying that re-read table failed with error 16:device or resource busy.next time i attempt to mount the newly created partition it comes error:mount /dev/sdx has wrong major or minor number.the same thing happens after i reboot the machine.can anyone give me a hand.

thanks in advance.

james