A few thoughts 1) Macro lenses often have a limiter-switch on them. This lets you limit the focus range that the lens will move through to either its long or close distances. This is so that when you're shooting normal distance subjects you can cut out the long range of close focusing distances. You don't need them and they are often quite fine on a macro lens; so cutting them out means you can focus quicker (there's less range to hunt through). If this limited switch is enabled for long distance and you try to focus close the lens can't achieve focus. On some the limiter affects manual focus as well and on others it doesn't. 2) When you focus closer on most macro lenses the aperture of the lens reduces. This isn't reported to the user (barring on Nikon lenses which do); but it means that the AF sensors are getting less light than if you were focusing at normal distances. Furthermore what is bright to our eyes can be very dim for a camera; indoors at night under normal indoor lighting is often bright enough for our eyes; but the camera will find it far more challenging. Thus a lack of light could be a factor. 3) AF at macro distances is hard because at those distances your natural body motions back and forth are very large shifts to the lens and its focal plane. As a result the lens and camera has to work extra hard and this can defeat many situations. It's why most macro photography is done with manual focus. Thus far Canon has attempted to improve on this with a hybrid IS system in their newest 100mm f2.8 macro and their newer camera bodies. 5) The lens you have achieves half-life-size which means that a subject reflected on the sensor by the lens is half the size it is in reality. This is half of what a normal "true" macro lens gets. As a result your lens shouldn't be having as much hunting problem as a normal macro at its closest focusing distance (though its still a challenge). As its sounds like macro is new to you chances are that its still operator error/inexperience playing a part here more than anything else.