Changes in uEnv.txt does not work

Hi,
I am Manish and i have recently started working on beagleboard xm. I am facing certain issues. Need guidance to solve it.

Background:
I am using beagleboard xm, uboot version 9 of 2011

Intention:
Current version of uboot has the environment variable loaduimage set for ext3 partition.Now i want the uboot to pick the uimage from fat partition. I can do it by modifying the uboot code and use the rebuilt uboot but i want to remove dependency on building uboot for future version. So i was trying to play around with uEnv.txt

Exercise:
Initially i tried to update loaduimage to fatload mmc ${mmcdev} ${loadaddr} uImage and tried booting but was unsuccessful.
I tried to uncover the problem by echo statements to track the code flow. I observed that the
1.Same command works when i change the omap3_beagle.h and rebuild the uboot but it does not work if i change it using uEnv.txt.
2.Also that the error is returned from mmcboot->bootm command saying the image is in wrong format. But i am using the same image as in case 1.

Can some on guide me how do i achive this. I want to use uEnv.txt for better maintanibilty

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What are the contents of your uEnv.txt? With v2011.09 and uEnv.txt that contains:

fromuenv=true
loaduimage=silly

I see:
Hit any key to stop autoboot: 0 The user button is currently NOT pressed. SD/MMC found on device 0
reading uEnv.txt

31 bytes read
Loaded environment from uEnv.txt Importing environment from mmc ... Unknown command 'silly' - try 'help'
...

Tom