You are most likely importing an XML file that does not match the Flexi XML structure. Each system has its own XML structure; before importing XML into Flexi, it must be transformed into Flexi XML.
For more information, see the documentation:
Import XML in the application ends with an error
Error message during import: "The root element must be 'winstrom' or 'Flexi'"
Written by Lenka Haringerová