[Android] Error : Multiple dex files define

[2014-07-03 17:40:01 - Dex Loader] 
Unable to execute dex: Multiple dex files define Lcom/google/ads/AdRequest$ErrorCode;

[2014-07-03 17:40:01 - DemoActivity] 
Conversion to Dalvik format failed: Unable to execute dex: Multiple dex files define Lcom/google/ads/AdRequest$ErrorCode;

These err msg seems due to improper settings in "Java Build path".