Hi,

I try to debug:zipline algo and get error Usecols do not match names

from zipline.api import (history,  
                         set_slippage,  
                         slippage,  
                         set_commission,  
                         commission,  
                         order_target_percent)

from zipline import TradingAlgorithm  
from zipline.utils.factory import load_bars_from_yahoo

def initialize(context):

    set_slippage(slippage.FixedSlippage(spread=0.0))  
    set_commission(commission.PerShare(cost=0.01, min_trade_cost=1.0))  
    context.tick = 0

def handle_data(context, data):  
    context.tick += 1  
    if context.tick < 100:  
        return  
    prices = history(100, '1d', 'price').dropna()  
    returns = prices.pct_change().dropna()  
    try:  
        weights, _, _ = optimal_portfolio(returns.T)  
        for stock, weight in zip(prices.columns, weights):  
            order_target_percent(stock, weight)  
    except ValueError as e:  
        pass

end = pd.Timestamp.utcnow()  
start = end - 2500 * pd.tseries.offsets.BDay()  
data = load_bars_from_yahoo(stocks=['IBM', 'GLD', 'XOM', 'AAPL','MSFT', 'TLT', 'SHY'],start=start, end=end)

# Instantinate algorithm  
algo = TradingAlgorithm(initialize=initialize,handle_data=handle_data)

# Run algorithm  
results = algo.run(data)  
results.portfolio_value.plot()  

    raise ValueError("Usecols do not match names.")  
ValueError: Usecols do not match names.  

What is this error mean how can i fix it?