Try what I suggested. Plus, try your remote starter by standing somewhere you can see the dashboard. Does the cluster light up like it does when you use the key?

If your remote starter works by simply hanging a good key right next to the ignition switch, then that confirms it being the immobilizer.

Have you added a key lately? When you program a key to work, what you're REALLY doing is programming the CAR to accept the key. But if they didn't include the remote starter, it might not be recognized any longer.