Evil Beholder Mind Control query

[Fiach]

I don't know if this is the correct forum for this, so apologies in advance

I have an Evil Beholder and am doing the Pirate Kat quest in Portland.

Fighting the pirates, all I get is a "?" when I cursor over an enemy when I try to cast Mind Control. The enemies are Level 2.

Any idea what I am doing wrong? I can see no information in the enemy tooltip that says they are immune.

Thanks for any help.