Siphon Mana bugged

I was making a custom map and i decided to add the blood mage hero, when i tried using siphon mana on an allied unit it gave an error message that it must be used on enemies. The unit i tried to use the skill on has 70/100 mana so its supposed to work isnt it? I tried playing a melee map (echo isles) and it worked, but whenever I try using it on a custom made map it won't. Can anyone tell me how to fix this? thanks!

map must be "latest patch" cos this was added by patches

Thanks again for your help! sorry cant add to your rep anymore I just added one.