The online competition that started on Monday invites viewers to win five iBooks each day this week.
GMTV explained that the Web site's drop-dialler technology used to randomly select competition winners is not Mac compatible.
"We discussed a cross-platform drop dialler with several technology companies. The feedback we received forced us down the PC route, as it proved difficult to implement a reliable multi-platform solution acceptable to the majority of our users," the company stated.
GMTV continued: "This technology is still in its infancy and we are making every effort to introduce a dialler that will cover a wide range of platforms. In the meantime, we can only apologise to Apple users."