Nandroid Won't Work

I'm having trouble with my nandroid backup. I keep getting the error verifying partition sizes... E:Unable to mount /sd-ext +----------+-----------------------------+------+----------+----------+---+---+ | Mount | Block Device | fst | Size(KB) | Used(KB) | M | B | +----------+-----------------------------+------+----------+----------+---+---+ | | | mtd | 0 | 0 | 0 | u | | system | /dev/block/mtdblock4 | yaffs2 | 358400 | 253264 | 1 | f | | data | /dev/block/mtdblock6 | yaffs2 | 437888 | 206712 | 1 | f | | boot | /dev/block/mtdblock3 | mtd | 3072 | 3072 | 0 | i | | recovery | /dev/block/mtdblock2 | mtd | 4608 | 4608 | 0 | i | | cache | /dev/block/mtdblock5 | yaffs2 | 163840 | 70744 | 1 | f | | sdcard | /dev/block/mmcblk0p1 | vfat | 14308593 | 6010216 | 1 | n | | | | | 0 | 0 | 0 | n | | andsec | /sdcard/.android_secure | vfat | 15640 | 15640 | 0 | f | | sd-ext | /dev/block/mmcblk0p2 | | 0 | 0 | 1 | f | | wimax | /dev/block/mtdblock0 | mtd | 12288 | 12288 | 0 | i | | | | | 0 | 0 | 0 | n | | | | | 0 | 0 | 0 | n | +----------+-----------------------------+------+----------+----------+---+---+ E:Unable to compute target usage (1 partitions, 0 bytes) I:Set page: 'backup_done' I:Set page: 'backup_failed' I:Set page: 'main' I:Set page: 'advanced'