Change Assistant error - "Failed to parse Change Package"

My target environment is on PT8.53.02.  FSCM 9.2.007 is packaged using PT8.53.12.  Change Assistant used is PT8.53.12 from the image.  Using FSCM9.2.007, I created a change package containing all fixes not yet applied.  Change Assistant processed this change package without any issues.  I modified the template to include customizations - add chapters/tasks/steps, and change step properties for a few delivered steps - to apply the modified change package to a different target environment, at which time Change Assistant throws the error message "Failed to parse Change Package".  I am unable to find any documentation about this error.  Has anyone seen