Try removing the / between Root and Templates. It should probably be
D:/01 - Spiele/SteamGames/SteamApps/common/Divinity - Original Sin/Data/Public/MageFire_63725dce-da32-4474-89e7-722b6f02febc/RootTemplates/MageFire.lsb
Edit:
Yep, that's most likely your problem. I recreated your issue by making my own Root/Templates folder and trying to save there.
Last edited by Rhidian; 01/08/14 06:30 PM.