Conflicting global spells??

[Adeptrain]

Hi,
I had a quick question to ask those more experienced in the game then me about global spells.

I'm currently playing the world map with Tien Chi and have Gift of health, the eyes spell, the fire gem spell, and mother oak global spells up. The problem arises when I try to cast any other global spell like the air domain spell that hits various high dominion provinces with lightning or the darkness spell. I get the message that the spell couldn't overcome a global spell already up or something....is there a limit to the # of global spells or do some of them conflict??
Oh, and I have to say I have NEVER come across a more helpful forum then this one in regards to a pc game