Problems with PASSLOCK II on 2003 Impala?

I have a 2003 Impala. The car starts and runs normaly. After running for a while, sometimes right after I start it, the message screen shows "SECURITY". When the light comes on I hear a click, like a solonoid activating. When it clicks the headlights and the dash lights flash. It continues to click once in a while during driving. The lights flash with each click.

I had one instance where the car wouldn't start. I tried several ways to "reset" the security system. The dealer said turn the key to run for 10+ minutes. This didn't work. I pulled the headlight switch in and out and it started. It's started everytime since then and functioned like I described in the paragraph above.

I'm confused, please help!