Pro-Form 500 TL runs 25 mins then stops cold?

My Pro-Form 500 TL runs 25 mins then stops cold.
I replaced the tread about a month ago. I have been using it about 5 days per week. I walk at a pace of about 3.8 miles per hr. Last week the machine started with this problem. All electronics remain on. The timer continues to mark time. The other indicators remain on.
A few days ago I applied a tread lubricant to see if that would resolve the problem. It worked for one 30 minutes session, but today it stopped at 26 min. Any ideas?

Duane S
September 2008