Why can't I pose my armature after setting a keyframe? I'm trying to use the Dope Sheet to animate a model I made, but after setting one keyframe (LocRot using the i key shortcut) any attempt to move any bone afterwards results in the bone being moved back to the position in the that one keyframe.
Make sure you are editing the bone and adding the keyframes in Pose Mode. 


Go to the starting frame.  
Make the Location/Rotation change you want on the bone 
Press the i key and select Loc/Rot


This establishes your starting position and rotation.


Go to the end frame.
Make the Location/Rotation change on the bone.
Press the i key and select Loc/Rot.


This establishes your end position and rotation

Your animation should play as expected.