不知道为什么我一直加载不了activiti插件，我同学JDK是32位的，他的可以，我JDK64位下的也是64位的 但是死活装不上，报错原因：
An error occurred while collecting items to be installed
session context was:(profile=epp.package.jee, phase=org.eclipse.equinox.internal.p2.engine.phases.Collect, operand=, action=).
HTTP Server 'Service Unavailable': http://activiti.org/designer/update/plugins/org.activiti.designer.eclipse_5.18.0.201508100929.jar
HttpComponents connection error response code 503.
An error occurred while collecting items to be installed
session context was:(profile=epp.package.jee, phase=org.eclipse.equinox.internal.p2.engine.phases.Collect, operand=, action=).
HTTP Server 'Service Unavailable': http://activiti.org/designer/update/plugins/org.activiti.designer.eclipse_5.18.0.201508100929.jar
HttpComponents connection error response code 503.
