Bit late in replying, but we have been getting the same wing/stab a-ice fail messages when checking the anti-ice system first flight of the day. Monitoring them over time, a pattern developed and they seem to appear on those days when the apu has been running a pack beforehand, usually if the engineers got out to the aircraft before us. The check requires you to ensure APU bleed closed, but the messages appear as if there is still some residual air in the system. If the first flight anti-ice check is done before any APU bleed air has been used, the fail messages dont seem to be dispalyed.