被这个问题虐了好几小时。
出错原因几乎和他一样，但一直找不到具体在哪：
http://stackoverflow.com/questions/15057273/duplicate-symbols-for-architecture-i386-and-couldnt-find-same-name-of-class-and
解决：
Go to Project Target-> Build Phases->Look for multiple occurrences of same file under "Compile Sources".
You can search for file name there as well.
Remove multiple occurrences from there.