Hi,
I once had a similar problem, I was doing something daft like powering an LED between the IR Detector Vcc and Vout and I had forgotten the resistor or hadnt cut the track under the resistor anyway the thing worked just not very well and not all of the time.
Other people will tell you that using a 9 volt battery is daft and they are generally right, its ok for powering the Arduino, but isnt up to powering whatever additional hardware you have. A common low cost solution is to use AA Batteries for additional components.
Duane B