I got an Axiom49 and mine works perfectly fine with FL Studio.
First make sure you installed all the driver software first off the CD.
Then turn on the power to the midi controller before you load up FL, then after, once within FL Studio go to:
Options-Midi Settings-Input, then highlight "USB Audio Device," the top one, then click on the little "Enable" button, then close that midi settings box down.
That's it, it should work.