[Yaffs] mount of empty yaffs2 fails

I'm trying to add yaffs2 to an omap2430 which has large block NAND and
OneNAND. I used flash_eraseall on a partition then tried to mount the
empty partition as yaffs2.
# mount -t yaffs2 /dev/mtdblock8 /mnt/yaffs2
mount: mounting /dev/mtdblock8 on /mnt/yaffs2 failed

Yaffs debug is enabled but this is all I get as an error.
What am I missing?

Thanks.

#cat /proc/filesystems
nodev   sysfs
nodev   rootfs
nodev   bdev
nodev   proc
nodev   debugfs
nodev   securityfs
nodev   sockfs
nodev   pipefs
nodev   futexfs
nodev   tmpfs
nodev   inotifyfs
nodev   eventpollfs
nodev   devpts
        ext3
        ext2
nodev   ramfs
nodev   nfs
nodev   nfs4
nodev   jffs2
nodev   unionfs
        yaffs
        yaffs2
nodev   mqueue
nodev   rpc_pipefs

and I enabled debug for yaffs.
# echo all>/proc/yaffs
new trace = 0xFFFFFFFF
+allocate
+always
+bad_blocks
+buffers
+bug
+checkpt
+deletion
+erase
+error
+gc_detail
+gc
+mtd
+nandaccess
+os
+scan_debug
+scan
+tracing
+verify
+verify_nand
+verify_full
+verify_all
+write
+all
+none