关键字：eclipse unbound "plug-in dependencies"
搜索引擎：google
This morning when I opened my Eclipse workspace, one of my RCP projects had ... that is normally called 'Plug-in Dependencies' was labelled 'org.eclipse.pde. core.requiredPlugins (unbound)' and the container was empty.
其实，这个workspace下存在sms[localhost]和sms_myself两个project，实际呢，这两个是同一个，只是project名字不同，其里面的包、类、应用库都是相同的，只不过sms[localhost]是书本配套的源码，而sms_myself是自己练习开发用的！
无意之中发现，当这两个project中其一发生"unbound"的问题时，删除其一，则"unbound"的问题就迎刃而解！所以后来我就把重新开一个eclipse来打开源码sms[localhost]，此后两个project相安无事，再也没有"unbound"!
From: http://weaklyreachable.blogspot.com/2006/01/eclipse-plug-in-development_7029.html