Why is this happening?

This keeps on coming up when I start to work on my project. I really haven't changed much to the code, and I have tried to undo everything I've done to cause this. I have never seen this error before, so could someone explain what's going on, and how to fix it?
If it helps, this is an update form, it downloads a text file, compares it with the current version, and if it's different, it downloads the new version, and starts it when it's done downloading and extracting. If anyone needs to see the code, I can setup a teamviewer meeting if you like.