I2c communication: wire.endTransmission() problem

I am using I2C communication to talk to the RTC chip(Real time clock). I am using this code for it http://wiring.org.co/learning/libraries/realtimeclock.html.  I am using Wire library given by Ti. For some reason it hangs at Wire.endTransmission(). Would you have any insight on that? Thanks for your support!!

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