The check sum for 5.1.1.2104 seems to be
c2b954790aceac52e496ae8fe964627f.If its a different version, you will need to go here and look at appropriate image version and try to download it and in the download page,it will show the md5 checksum.
http://www.cisco.com/cgi-bin/tablebuild.pl/callmgr-51
HTH
Sankar
PS: please remember to rate posts!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus