“Content is not allowed in prolog” when parsing perfectly valid XML on GAE

Question

I\'ve been beating my head against this absolutely infuriating bug for the last 48 hours, so I thought I\'d finally throw in the towel and try asking here before I throw my

Answer 1

Unexpected reason: # character in file path

Due to some internal bug, the error Content is not allowed in prolog also appears if the file content itself is 100% correct but you are supplying the file name like C:\Data\#22\file.xml.

This may possibly apply to other special characters, too.

How to check: If you move your file into a path without special characters and the error disappears, then it was this issue.