Hmmm… hjt… quick search indicates that file type is used by PIM software.
Error reading first article/node with ID = 0
Invalid data found in file
One presumes that error is coming from said PIM software, and not Notepad++ itself. It sounds like you’ve done something to screw up your file.
I don’t think anyone here will be able to help; you are likely really close to baking up some cookies.