This is usually caused by either a bad door switch, a loose door switch mount, or a problem on the control panel.
Even though a door switch clicks, it may still be bad inside. Its continuity must be checked.
Door switch or mount trouble can be caused by slamming the door or by opening the door while it's cooking without hitting the Stop pad first.
If you or someone you know decide to look into it, we have critical information on safety, disassembly and door switches at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk
You can find helpful exploded view diagrams and order parts by entering your full model number here: http://www.searspartsdirect.com
A full Sears/Kenmore model number usually has 3 digits, a dot, then 8 more digits, such as ###.########
If you think the problem is on the control panel, we repair these nationwide by mail for $39.95 postpaid in most cases.
We're happy to help and we appreciate your thoughtful rating of our answer.
William E. Miller, AS-EET