Why am I getting an “Unknown error” message? I am using Acrobat Pro 11 to import an XMP file to a PDF. The XML is valid. The XMP file contains parent and child metadata coded in XML? I have several article titles as parent metadata entries and their respective corresponding authors, page numbers, and abstracts as children. This is one single file because the single PDF document contains multiple articles. When I go to import the XMP file, there is a error popup stating "Unknown error". Is there a way around this issue? I've tested several other XMP files with parent child relationships and the error happens on all of them. But, when I only use one level (e.g., parent) the XMP file is able to be imported without issue.