The following can be reproduced on Mac and Linux, with LO 4.3.5.2 and 4.4.2 (official website downloads), by loading a LaTeX document. I used this one: http://www.math.duke.edu/computing/tex/templates/samplefile.tex ~ > /Volumes/LibreOffice/LibreOffice.app/Contents/MacOS/soffice :1: parser error : Document is empty \documentclass{article} ^ Just load the .tex file into Writer and the output is being dumped to the terminal. Renaming the .tex file to .txt "fixes" this problem. Despite the output, the document is loaded into Writer. I expected LO to load the plain text file silently; however, this misleading warning seems to indicate that there is a problem with the loaded document.
The message comes from libxml2. It means that, during format detection, one of the import filters tries to check if the input is XML. Which it is not, so libxml2 rejects it. The message is otherwise harmless. Furthermore, it does not come from libreoffice's code, but from one of the import libraries, because libreoffice uses expat as XML parser, not libxml2. If you can identify which one it is, report a bug for it.