IK rigged limb not bending at joint

I’m having a problem with an IK rig. There’s an upper arm, a lower arm, and a target and pole handle. I have the constraint set up correctly, but no matter how I move the handle the arm won’t bend at the elbow. It remains perfectly straight no matter where the handle goes.

Here’s the modifier as I applied it. Am I missing something? I made this particular test in v2.66, but it’s happening in the newer version too.

remove the pole target.

add a second ik to the upper arm, chain length just 1 and use the pole target bone as the target for that second IK.