Stuck on the Getting NASDAQ Symbols module!

Stuck on this module:

My code (see below) is exactly the same as that given in the solution, but I kept getting the error " Expected symbols to be a DataFrame containing NASDAQ stock symbols." Why?? HELP PLEASE!!

import codecademylib3_seaborn

from pandas_datareader.nasdaq_trader import get_nasdaq_symbols

symbols = get_nasdaq_symbols()