booting router from tftp: image is stored within a sub-dir in tftp root

Hi

I have a 7200 series router. Image version: c7200-is-mz.123-6f.bin
I want to boot it from tftp.

The config register is set to 0x0 and the router is in rommon mode.
I use the following command:
rommon> boot <image name> <tftp ip>

The router boots successfully from the specifed image.

The image is stored on the tftp server as :
/tftpboot/<image name>

However, if the image is stored in a sub-directory on the tftp server
and the sub-directory as well as all files/dirs inside it have 777
permission, and the command is:
rommon>boot sharad/<image name> <tftp ip>

the router does not boot up.
I also tried,
rommon>boot /tftpboot/sharad/<image name> <tftp ip>

The image is stored as:
/tftpboot/sharad/<image name>
but it does not work.

Any idea, how do I boot the router from tftp and pick up the image
from a sub-dir in tftp root directory.

Any info will be appreciated.

TIA
Sharad