Seeing as I have now worked somewhat the SQL XML Bulk load, I have decided to start compiling a list of the errors I got and what I did to solve them to help myself (and others) the next time I encounter one of these errors.

The statement has been terminated.
This usually means some SQL Error has occurred within the bulk load, for example a wrong data type, truncating of data and so on.
Check the ErrorLog file for more information.

Schema: the relationship XXX referred to in the node 'YYY' is not defined.
This means – as the error says – that a relationship is missing in the schema file. Usually more often than not, this means I’ve misspelled something in my relationship definitions or where I use the relationship. Otherwise make sure your relationship is defined if it is missing.

Schema: the annotation 'field' on the empty content element 'XXX' is not supported.
The “field” annotation is set on what is a container tag. You can’t assign a field to a container tag, but it needs to be set on an element.

Schema: the parent/child table of the relationship on 'XXX' does not match.
This for me usually means that I’ve forgotten to add  the relation on the field which has a relationship, or that I’m accessing the wrong tables.

The column 'XXX' was defined in the schema, but does not exist in the database.
Well, obviously, this means that there’s a field mapping in the schema file which doesn’t match the database. Check the spelling of the field/column name in the schema file.

Invalid character value for cast specification.
This means that you’re trying to make an invalid cast, for example trying to cast a string into a number field.