It is likely that you neglected to set the weights of the moves in the book and that all of the moves' weights are set to 0, meaning they will never be chosen by a computer personality. If you created your book "by hand" (rather than using the "Import PGN" feature), then this is probably the case. If you set the weight of all of the moves to 100, then no move will ever be ignored. If there is more than one move available for a given position, then the chances that a particular move will be made are based on that move's weight AND the weights of all of the other moves for that position. The formula is to add up the weights of each of the moves and then divide each INDIVIDUAL move's weight by the total to determine the percentage chance that a move will be selected.
-- In response to 1.e4, you have the choices 1...e5 and 1...c5, each with a weight of 100. This means that 1...e5 will be chosen 50% of the time (100/200) and 1...c5 will be chosen 50% of the time (also 100/200).
-- Let's say you add 1...d5 as another response to 1.e4 (in addition to 1...e5 and 1...c5 above), but you give it a weight of 25. This means that 1...e5 and 1...c5 have about a 44% chance (100/225) of being made, and 1...d5 has about an 11% chance (25/225).
Once again, note that moves with a weight of 0 will NEVER be selected by a computer personality.