any other error inside the session log?
does it work if you remove Hierarchy transformation? (to validate it's a source problem or transformation problem)
Looks like something is not done properly as part of IICS, I would revisit all config once again.
Between: I look for other options like convert xml to .csv using command line and use to load. as long as its about dumping data from here to there.
This error comes when the hierarchy parser is not able to convert it/corrupted.
Please try once by recreating the parser again.Also please attach the session log for further verification.
Also please verify the cardinality of the elements.