Hmm its been a while since Ive been inside one of these. If I recall correctly there are some plastic clips which act as stops to prevent it being wound too fine. However unless theyve been moved from their original location it should have been able to grind finely enough at some point, and if it cant now it would normally indicate wear, either in the burrs or in the housing. If youve got a couple of screwdrivers its not hard to get the lid off.
shows one of the Phillips head screws which holds the grinder in position, just below the pump and to the left of the water tank (NOT NOT NOT the one circled - thats the one you have to remove to change the tamper, which was the original purpose of that photo!). If you look through some of the other photos on http://www.coffeetamper.com.au/products/vanilla-installation-guide.html you can see a couple of other shots although theyre not intentionally of the grinder so theyre only lurking in the background. Anyway with the lid off you should be able to turn the adjustment knob and see whats stopping it, and also see whether theres any obvious reason why its not grinding fine enough (perhaps something else has gotten in the way of the adjustment mech so it cant go all the way now?)