I have seen the same behavior with the 48lvl,
It appears that certain things are immune to charm (some names some other non names) and the way you can find out is by seeing those anoying messages,
And yea if they want it to work like they they should have mentioned it in the spell!!
Otherwise I try to bug it every time i get it because some of the things it did not work on i can see no reason and for whatever reason if they want it to work like this then the spell should cast but you get an immune like if you try to hit with a weapon that the creature is immune too
SOE strikes again
Another notch marked in the soe bugs/anoyance pole, dang i am running out of space