See this question on SO: http://stackoverflow.com/questions/10373077/tomcat-7-severe-a-child-container-failed-during-start There is a problem scanning a class but no info on which one. It could be fault input of BCEL could need updating for a newer Java version. If the error message identified the class triggering the problem, it could be analysed. A better error message is required that names the class having the problem.
Fixed in trunk and 7.0.x and will be included in 7.0.28 onwards.