The problem is that you're including a webpage, being requested as such.
You need to include the file directly:
// or, if you're working in - say - 'folder2' (which resides next to 'folder'):
Or you could use the absolute path to the file:
Note that this last version will be problematic if you ever change the folder layout of your website or move to a different host, as you may have to change all your include statements.