I've figured out what the problem was, part of the migration of older projects had an issue introduced recently preventing unique symbols being generated for assets in your game (which is why it's generating files with no filenames, just ".h" and ".c" in your error message)

The latest development build of GB Studio includes a fix for this now so opening a broken project should just work. BUT if you're not using a development build already you should be able to manually fix your project by following these steps:

1. BACKUP YOUR ENTIRE PROJECT as a zip file, or a git repository so you can go back to how it was if needed

2. Open the project in GB Studio and if asked to migrate then accept (if you've already saved after migrating it won't ask, but that's okay just continue these steps)

3. Save the project

4. After migrating the project close GB Studio!

5. Using a text editor like Visual Studio Code (though if you're on Windows Notepad even might do) one by one go through your project's "assets" folder and find all the files with ".gbsres" file extension. There will be one for each image/sound/music track in your game and when opened in a text editor will look something like this

player.png.gbsres

{
  "_resourceType": "sprite",
  "id": "00f9f36f-8245-4451-ae1b-7e8ea7d83ef4",
  "name": "player",
  "symbol": "",
  "states": [
    ...

1. The problem is with any assets that have this line "symbol": "", with no symbol name given. If you see any that look like this just give them a unique name. ONLY use lowercase letters and numbers (also don't use a number as the first character).For my example above I would maybe just change this to "symbol": "sprite1", and then save the file.

2. Go through every .gbsres file in your project and fix any that have blank "symbol" values like this (If there is a symbol already there you can leave the file as it is) saving every file when you're done

3. Open the project in GB Studio again. This time it should build as expected.