I ran into this error and I got it resolved. Within the xml file, there is a reference to a .xsd that defines what the schema of the xml should be. In my case, i ran into the error when carrying out settings migration. So the settings.xsd schema has the definition.
Copy the entire xml and paste in an xml validation website. In my case, i used: http://www.xmlvalidation.com.
It will prompt you to copy the referenced .xsd file and paste in as well.
Doing this pointed to entries that had "-" in it. The .xsd file did not expect entries with a "-" as it broke the wildcard regex.
I solved it by removing those entries and replacing them with a wildcard instead.
For Example
ewcartreminder-1/title/name.
I replaced the entry with ewcartreminder*
Hope this helps someone.
