# What constitutes a “context” in Pose mode?

I have an armature associated with a mesh. In Pose Mode I have oriented the armature the way I want, so I press A to select the entire armature and then I press I to insert keyframes. I've done this successfully on simple models while following tutorials, but back in my real model I'm getting the following error and I don't understand what context is being looked for.

No suitable context info for active keying set

What constitutes a "context" in Pose mode? What should I be looking for in my model structure that is leading to such an error?