Could you just check that you aren't accidentally attempting to uncompress a same image twice (once on the sender (image server) and once on the receiver?). This will fail because at the first decompression, the data is not longer a compressed archive, and will no longer match a checksum. Usually, in the interest of bandwidth, decompression should be done on the workstations to be imaged (receivers), and not on the image server. That is, on the image server, you should not use a "-p lunzop" option or something similar.
Regards,
Alain