Why not use ChannelPlaying() instead of using a separate var:
mySound=LoadSound("mySample.wav") LoopSound mySound While Not KeyHit(1) If KeyDown(57); SPACE KEY If Not ChannelPlaying(myChannel) myChannel=PlaySound(mySound) EndIf Else If ChannelPlaying(myChannel) StopChannel myChannel EndIf EndIf Wend FreeSound mySound