strange rotation

I have a problem with my animatin.

This is the scene:
(the text says “Child” and “Parent” The left object is activated)

Now i want the left arm to move down. So i make a rotation keyframe go 50 frams forwad rotate around the global X axis and make a second keyframe.

but if i play the animaton i see this (frame 25): view
(the arm at the lower part of the picture is the left arm on the firdt pic)

The arm somehow bends to the right but goes back to the wanted position at frame 50.
how can i change this? is it becouse of the local axis are difrent frome the global? if yes: how can i corect it?

(sorry for my bad english spelling)

problem solved. i just cleard the parents and made it new. now it seams to work.