Android_SDK4.2_ (API17) _Eclipse3.8 development environment src folder encounter problems

red cross Android_SDK4.2_ (API17) _Eclipse3.8 development environment encountered problems src folder red cross
hope to have great God answers, thank you .
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project is not associated with the sdk it
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build path
look into the package which is not there with a red cross , are generally not copy copy jar package engineering reasons
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without any log, without any description of the error , can help you really only god. . . .
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