PRU analog pin access Failure to resolve tree message

I am on Ubuntu 12.04 using 3.8-13 Bone 20. I have the new dtc which compiles the -@ symbol without errors. When I try to echo into the slots file I get a failure to resolve message in dmesg.
Which kernel does work? I can access digital pins - the argonne lab exercises 0 through 3 work. The slots file shows the first 4 hex codes displayed. attempts to load precompiled dtbo files fail with the same failure to resolve device tree message.

Is there some step I am missing? Different or kernel patch?

root@ubuntu-armhf:/lib/firmware# uname -a
Linux ubuntu-armhf 3.8.13-bone20 #1 SMP Wed May 29 10:49:26 UTC 2013 armv7l armv7l armv7l GNU/Linux

ubuntu@ubuntu-armhf:~$ cat /sys/devices/bone_capemgr.9/slots
0: 54:PF—
1: 55:PF—
2: 56:PF—
3: 57:PF—

root@ubuntu-armhf:/lib/firmware# echo am33xx_pwm > /sys/devices/bone_capemgr.*/slots
bash: echo: write error: Invalid argument

dmesg | tail

[ 376.227327] bone-capemgr bone_capemgr.9: part_number ‘am33xx_pwm’, version ‘N/A’
[ 376.227495] bone-capemgr bone_capemgr.9: slot #6: generic override
[ 376.227543] bone-capemgr bone_capemgr.9: bone: Using override eeprom data at slot 6
[ 376.227594] bone-capemgr bone_capemgr.9: slot #6: ‘Override Board Name,00A0,Override Manuf,am33xx_pwm’
[ 376.227860] bone-capemgr bone_capemgr.9: slot #6: Requesting part number/version based 'am33xx_pwm-00A0.dtbo
[ 376.227913] bone-capemgr bone_capemgr.9: slot #6: Requesting firmware ‘am33xx_pwm-00A0.dtbo’ for board-name ‘Override Board Name’, version ‘00A0’
[ 376.227966] bone-capemgr bone_capemgr.9: slot #6: dtbo ‘am33xx_pwm-00A0.dtbo’ loaded; converting to live tree
[ 376.228512] bone-capemgr bone_capemgr.9: slot #6: Failed to resolve tree

root@ubuntu-armhf:/boot/uboot# more uEnv.txt

optargs=fixrtc
cape_enable=capemgr.enable_partno=am33xx_pwm-00A0,bone_pwm_P8_13-00A0
loadfdt=ext4load mmc ${mmcdev}:2 ${fdtaddr} /boot/dtbs/${fdtfile}
loaduimage=mw.l 4804c134 fe1fffff; if ext4load mmc 0:2 ${loadaddr} /boot/zIm
age; then mw.l 4804c194 01200000; echo Booting from external microSD…; set
env mmcdev 0; else setenv mmcdev 1; if test $mmc0 = 1; then setenv mmcroot /
dev/mmcblk1p2 rw; fi; ext4load mmc 1:2 ${loadaddr} /boot/zImage && mw.l 4804
c194 00c00000; echo Booting from internal eMMC…; fi
mmcboot=run mmcargs; bootz ${loadaddr} - ${fdtaddr}
uenvcmd=i2c mw 0x24 1 0x3e; run findfdt; if test $board_name = A335BNLT; the
n setenv mmcdev 1; mmc dev ${mmcdev}; if mmc rescan; then setenv mmc1 1; els
e setenv mmc1 0; fi; fi; setenv mmcdev 0; mmc dev ${mmcdev}; if mmc rescan;
then setenv mmc0 1; else setenv mmc0 0; fi; run loaduimage && run loadfdt &&
run mmcboot

Thanks.