This might seem weird, but make sure your keyframe slider is at frame 1 or what ever you use for the first frame (some people use 0). I had that same issue that the first time it worked but the second time it wouldn't, having it on frame 1 before playplasting always worked for me. Also make sure to turn off any background apps like media players (I tend to listent to music when I work.) That might help out in the speed department. I hope this helps in anyway, and if you have a good rigging solution for a holster let me know.