Error in Pandas 0.25 on pd.drop_duplicates()
Pandas 0.25.1 
Python 3.6

I am attempting to use Pandas.drop_duplicates() in Anacadona, Jupyter Notebooks, by considering only a certain subset but am getting an error KeyError: Index(['days'], dtype='object')

The Index is as follows: `id, event_description, attribute1, attribute 2, attribute 3, days, days_supply, days_equivalent`

I want to ignore attribute 2 and attribute 3 so I have ran the following:

```python
df = df.drop_duplicates(subset=['id', 'event_description', 'attribute1', 'days', 'days_supply', 'days_equivalent'])
```
Which returns:
```python
eyError                                  Traceback (most recent call last)
<ipython-input-4-3f7da32b380f> in <module>
      7 
      8 df = df.drop_duplicates(subset=['id', 'event_description', 'attribute1', 'days', 
->    9 'days_supply', 'days_equivalent'])
     10 
     11 print(df)

/anaconda3/lib/python3.6/site-packages/pandas/core/frame.py in drop_duplicates(self, subset, keep, inplace)
   4892 
   4893         inplace = validate_bool_kwarg(inplace, "inplace")
-> 4894         duplicated = self.duplicated(subset, keep=keep)
   4895 
   4896         if inplace:

/anaconda3/lib/python3.6/site-packages/pandas/core/frame.py in duplicated(self, subset, keep)
   4949         diff = Index(subset).difference(self.columns)
   4950         if not diff.empty:
-> 4951             raise KeyError(diff)
   4952 
   4953         vals = (col.values for name, col in self.items() if name in subset)

KeyError: Index(['days'], dtype='object')
```
Once I remove days, the remove duplicates runs without flaw, but I do need to make sure I consider days. What does the error require that I fix?
