Import Data Problem

Hello, I got one problem here, when I import data from excel file, the value for "May 1" been changed to "April 30", and "July1" become "June 30". This problem occured when I import data into RapidMiner Server repository folder, but, when I try import the same data into Local Repository, the data remains as original one.

Somebody please help me, I am an intern student and very new to RapidMiner.