The type editor throws an EXCEPTION when trying to create a type from an XSD.

Example:

Notification(Error):
Error during translation ..\FILENAME.xsd
Error in file file:///C:/../FILENAME.xsd, Line: 35, Pos: 11:
The ...Extensions element was not declared.

This is an indication that the missing element specification is defined in another XSD file, but the resource is not available.
It is also possible that the specification is inconsistent, incomplete or missing.

Make sure that the paths of the dependencies specified in the XSD are accessible ¹⁾ or available.
Try to get a full specification of the type to build and try again.