"The character configuration file, <filepath/filename.xml> was invalid"
In Retargeter Character Setup or Open Performance, attempting to load a character setup .xml file that is not a correctly formatted file. This most often occurs from attempting to load a .xml file that was not created in Retargeter Character Setup.
Only use character setup files that have been created in Retargeter for use with your current character.
For more information about Character Setup in Retargeter, see the following article: Character Setup: Part 1 - Control Setup