My daughter just showed my the airdrop feature, better late then never I guess. Be that as it may, airdrop is working with all my devices except my iMac. Any idea why? On my macbook when i click airdrop in finder at the bottom is shows the 'allow me to be discovered by option" but on my iMac it just says "to share with someone using a mac, ask them to go to airdrop in finder" why am i not getting the option to choose to to allow to discover me?