Issue with Reading/Writing into XML Files

Don't include the XML file in your project, or change it so that's it's not automatically copied to the output directory. Then you'll need to modify your app so that it can handle the case where the file doesn't exist yet and create it with some default values in it. If you want to include the config file with your app when you deploy it to another PC then you can include that file when you build the setup and deployment project.

If you specify the full path to a file and then that file doesn't exist, an exception may thrown when you try to load it. I say may because it depends on the exact way you're doing the loading - some ways throw and others don't. A null ref exceptions sounds like the load operation is returning null and then you aren't checking the document variable for null before using it.

Also this sounds like a file that should be stored in the App Data or Local App Data folder, not alongside the executable. If your app is deployed to the Program Files directory then you'll have problems reading and writing it without granting unnecessary privileges to your app.