This can happen sometimes if you don't get the hole drilled exactly down the center of the aileron or if the hole is drilled too deep. Also if the aileron is "twisted" on against the linkage. Heck, it's just balsa. Whenever you drill one of these holes and are satisfied with the fit, go ahead and "toughen" it with a little CA. Let it cure well before putting the linkage back in the hole. You may need to freshen the hole with a drill afre the CA.