Hey jaketakelake. I think you're misunderstanding how the JSON object works. JSON is a format for expressing arrays in a string.
When you tell Construct to "Load from JSON string" you are supplying the value "examplelevel.json". However, this doesn't actually have anything to do with the file in your Files folder. It's just a literal string, so Construct attempts to parse "examplelevel.json" - which isn't a valid JSON string in itself - and unsurprisingly nothing happens.
So, what are your options? You have two as far as I can see. You can use the AJAX object to request a JSON string from a PHP page, and store your levels in a server somewhere. This is a fairly simple solution if you have access to a server.
Alternatively, if you are developing for desktop, you should be able to use Node-Webkit's File IO functions to retrieve the contents of your level.
To reiterate: The Load JSON action requires a JSON string, which right now you are not providing. There is no way that I am aware of to access this file when it is in the Files folder.