Yahoo does not return bid/ask on some symbols for their delayed quotes. There is nothing we can do about it. For example, here is a CSV response
"ETFC",20.16,20.15,20.16,20.18,19.83,"1/3/2014","12:35pm","E*TRADE Financial",19.86,19.81,1365954,19.86,9.09
"C",N/A,N/A,53.04,53.19,52.31,"1/3/2014","12:35pm","Citigroup, Inc. C",52.39,52.27,14251982,53.68,40.28
"BAC",N/A,N/A,16.47,16.50,16.23,"1/3/2014","12:35pm","Bank of America C",16.27,16.10,82193576,15.98,10.98
"SCHW",N/A,N/A,25.87,26.04,25.70,"1/3/2014","12:35pm","Charles Schwab Co",25.84,25.82,1547284,26.08,14.98
"IBKR",24.35,24.34,24.35,24.71,24.26,"1/3/2014","12:34pm","Interactive Broke",24.46,24.52,165885,25.03,13.57
"GS",N/A,N/A,178.04,178.67,176.22,"1/3/2014","12:35pm","Goldman Sachs Gro",176.35,176.89,944738,178.38,130.32
"TWTR",N/A,N/A,69.6901,70.43,68.432,"1/3/2014","12:35pm","Twitter, Inc. Com",68.95,67.50,21510576,74.73,38.80
"GOOG",1108.67,1108.1801,1108.4301,1116.9301,1105.27,"1/3/2014","12:35pm","Google Inc.",1115.00,1113.12,813324,1121.00,695.52
"FB",54.86,54.85,54.85,55.65,54.61,"1/3/2014","12:35pm","Facebook, Inc.",55.00,54.71,25396320,58.58,22.67
"AMZN",397.85,397.63,397.72,402.71,397.00,"1/3/2014","12:35pm","Amazon.com, Inc.",398.29,397.97,1146164,405.63,245.75
"AMTD",N/A,N/A,30.68,30.705,30.34,"1/3/2014","12:34pm","TD Ameritrade Hol",30.47,30.43,412502,30.73,17.46
"AAPL",543.66,543.56,543.55,553.70,543.036,"1/3/2014","12:35pm","Apple Inc.",553.00,553.13,7460859,575.14,385.10
Notice the N/A for some fields. Those are bid, ask