Do you have some strange characters in the file or something similar? The contents itself look okay to me. Did you change something in u-boot when compiling it such as removing support for extlinux or the like? At least these messages seem to indicate that uboot does not know what the commands in the extlinux.conf mean:
One thing you could try would be entering the relevant commands by hand on the command line and see if it boots then for you.
Code:
Retrieving file: /extlinux/extlinux.conf
191 bytes read in 2 ms (92.8 KiB/s)
Ignoring unknown command: MENULABEL
Ignoring unknown command: KERNEL
Ignoring unknown command: INITRD
Ignoring unknown command: DEVICETREEDIR
Ignoring unknown command: APPEND
One thing you could try would be entering the relevant commands by hand on the command line and see if it boots then for you.