The Great Peace March by more than 1,000 anti-nuclear activists was turned away from a school campsite in Claremont on the third day of a 3,235-mile walk across America, because of insurance problems. But local churches and residents opened their doors to participants marching coast-to-coast in a nine-month trek for nuclear disarmament. It was the first time the marchers were forced to alter their plans because of a lack of insurance required by Caltrans and some cities along the state route. The marchers had planned to spend the night on the athletic field at Claremont High School. Instead, about 10 area churches opened their facilities and offered housing in private homes, a PRO-Peace spokeswoman said. Both the City of Claremont and the Claremont Unified School District approved use of the Claremont High athletic field last week, but PRO-Peace didn't have the $5 million in liability insurance required by the district, said district business manager Ron Fortson.