I got this error when I press build+debug:
ld: duplicate symbol .objc_class_name_BlogTableItemCell in /Users/fabian/Development/Workspaces/iphone_experiments
iPhone: Duplicate Symbol Error? by user576924
answered it correctly for me. However to find the offending gremlin this ZSH snippet.
grep "import.*\.m" **/*.[hm]
Will immediately tell you where your error is.