Error when i tried accessing pandas dataframe index - python-2.7

Question

I used two csv files create a dataframe:
import matplotlib.pyplot as plt
import pandas as pd
#import data
df1= pd.read_csv("C:\Users\Meiji\Desktop\CNST 6308-python\Hourly_TTI.csv")
df2= pd.read_csv("C:\Users\Meiji\Desktop\CNST 6308-python\Weather.csv")
#standardize date format
df1['new_date']= pd.to_datetime(df1['Date'])
df2['new_date']= pd.to_datetime(df2['EST'])
#merge TTI and weather dataframe
df=pd.merge(df1,df2,on=['new_date'])
#plot
df[df["Events"]=='Rain-Hail-Thunderstorm'].groupby('Hour').mean()['TTI'].plot()
df[df["Events"]!='Rain-Hail-Thunderstorm'].groupby('Hour').mean()['TTI'].plot()
plt.ylabel('TTI')
plt.legend(['Rain-Hail-Thunderstorm','Ohters'])
plot.show()
Here is the error I'm getting:
Process started (PID=27504) >>>
Traceback (most recent call last):
File "C:\Users\Meiji\Desktop\CNST 6308-python\HW4\new 2.py", line 12, in <module>
df[df["Events"]=='Rain-Hail-Thunderstorm'].groupby('Hour').mean()['TTI'].plot()
File "c:\python27\lib\site-packages\pandas\core\frame.py", line 2927, in __getitem__
indexer = self.columns.get_loc(key)
File "c:\python27\lib\site-packages\pandas\core\indexes\base.py", line 2659, in get_loc
return self._engine.get_loc(self._maybe_cast_indexer(key))
File "pandas\_libs\index.pyx", line 108, in pandas._libs.index.IndexEngine.get_loc
File "pandas\_libs\index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc
File "pandas\_libs\hashtable_class_helper.pxi", line 1601, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas\_libs\hashtable_class_helper.pxi", line 1608, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'Events'
<<< Process finished (PID=27504). (Exit code 1)
what am i missing? My friend has a same code, but he run perfectly.