low light

Help...A300 low light focusing.

I am having trouble getting a low light focus lock on the A300. I am using a combo of kit, KM50mm 1.7 and SAL75-300. It doesn't seem to matter which lens I have attached. There is plenty of light to get great 1600-3200 shots but I can't get the focus. I tried w/ AF Illuminator in Off and Auto w/ no perceived change. I have tried leaving red eye reduction on/off w/ no help. I left the flash up while not using thinking it might give me the AF Illuminator but no help. Is this simply a limitation of the camera, or my lenses.