score_OBJECTIVE does not target

Added objective "Mjölnir".
I wanted to target a player with a score of minimum 1 of Mjölnir.
"Entity UUID provided is an invalid format" even I have a score fo 1
"score_Mjölnir_min=1" doesn't work, neither does "score_Mjölnir=1"

When I try to target me with a /tell command, it doesn't find me either. (See picture)