OK, here's the deal.
If you're having the same problem, go to the XMB > Settings > BD/DVD Settings
Scroll down to BD 1080p 24Hz Output (HDMI)
Set it to "Off"
I had mine set to "Automatic". But apparently, the "Automatic" setting isn't automatic.
Now the Blu-Ray movies are playing w/ no issue.
I guess the question is, how do you know when to set it to "On"? Or, how do you know if the BD (Blu-Ray Disc) is recorded at 24Hz?