well an update, apparently you get that error when you don't have the buff on (doh, lol).
So its working, but not correctly. It does not remove Spirit of the Lion Rk. I, but instead will remove any buff that is right next to it. tested with a few different random buffs. Any ideas?
if i /echo ${Math.Calc[${Me.Buff[Spirit of the Lion Rk. I].ID}-1].Int} (with the buff on) i get a number as the result which im assuming is supposed to relate to the buff slot that buff is in (if you do just a /notify BuffWindow Buff0 leftmouseup it removes the 1st buff) However the number i always get with ${Math.Calc[${Me.Buff[Spirit of the Lion Rk. I].ID}-1].Int} is never the correct number that buff is currently occupying.
I tried moving the buff around to different slots. the results are all over the place. when its in slot 11 i thinks its in 9, if you do a +2 it to compensate, it doesn't remove anything. A +1 works, which doesn't make sense either. However, when i moved the buff to slot 4 (counting from 0) and did a -1, it removed the buff #3. a -0 removed the correct buff. Now again more crazy b/c when i rebuffed and it goes into slot 3 now, i used the same -0 and it removed the buff in slot 1.... so i have no idea wtf is going on with this haha