The next thing to check is your application's communication log. This will log all communication occurring within your application, including authentication attempts.
As long as the device ID is correct or the key/secret are correct, the log will display a message with additional information. This is only a real-time log, so you'll first want to open the browser to the application overview page, then attempt to connect. If you don't see any information logged, this means both the device ID and the application key/secret are incorrect. Basically we couldn't figure out which application the device belonged to based on the authentication information provided.
You can also PM me your source code and I can take a quick look at the device ID, key, and secret to make sure they look correct. It's very common to have those swapped or copy/pasted incorrectly into the source code.