6027-2237 [W] An image backup made from the live file system may not be usable for image restore. Specify a valid global snapshot for image backup.

Explanation
The mmimgbackup command
should always be used with a global snapshot to make a consistent
image backup of the file system.
User response
Correct the command invocation to include the -S option
to specify either a global snapshot name or a directory path that
includes the snapshot root directory for the file system and a valid
global snapshot name.