Tomcat不是Myeclipse自带的，是从外部下载的
错误信息
A configuration error occurred during startup. Please verify the preference field with the prompt:Tomcat 7.x JDK name:
解决办法:
上面的错误描述就可看出是tomcat7 的jdk没有配置对
请检查你的jdk环境变量配置
window->preferences->MyEclipse->Servers->Tomcat->Tomcat 7.x->JDK