I use 9 the NRF24L01 from sparkfun : SparkFun Transceiver Breakout - nRF24L01+ (RP-SMA) - WRL-00705 - SparkFun Electronics with the right antenna 2.4GHz Duck Antenna RP-SMA - WRL-00145 - SparkFun Electronics
1 sender and 8 receivers and they work over 80 meters !!! without ant trouble.
Where did you bought yours ?