XML : Unknown error builder.parse(File f) - PARSE XML

I need to parse an XML file to write its content to a .TXT file and I'm using document builder.

The objetive is to parse the .XML line by line and write it to a .TXT ir order to retrieve all that info organized in the TXT to build some graphs.

As you can see below I'm getting an error and that does not even say what's the problem.

I think I'm making everything as it should be done. If somenone could help me would be great.

Thanks in advance.