Ran into this problem on about 3 hosts when upgrading from 5.0 to 5.5.
2 of the hosts were resolved following this KB:
KB basically states to check /altbootbank or /bootbank and move the file located in stage.xxxxxxx the the directory above it.
1 of the hosts required the KB above in addition to uninstalling the FDM agent by doing the either of the following:
Remove Host from HA (This removes the fdm agent, use command lines below if needed)