This behavior is definitely unusual as the recommendations by kvbarkley are spot on.
When you say that you cannot adjust the Highlight tone priority setting in the 1st red camera menu tab when in the movie mode, do you mean the menu option is grayed out or that setting it to disable doesn't make the D+ go away?
Are you able to post a screenshot of what the 1st red camera menu tab, when in the movie mode, of your camera looks like?
Even with Highlight tone priority enabled you should still be able to set the ISO between 200-6400, provided the Movie Exposure menu option is set to Manual.
In the movie mode, while not actively recording, what happens on the rear LCD when you press the ISO button on the top of the camera? If the ISO menu shows up on the rear LCD as it should when the ISO button is pressed, are you able to change the current ISO by rotating the main dial on top of the camera?
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I can't adjust the Highlight Tone Priority and ISO Speed setting increments setting because the menu option is grayed out.
Yes, I can't adjust the ISO too. The ISO menu appears when I pressed the ISO button on top of camera. The value of ISO stayed at 6400. When I rotated the main dial on top of the camera, nothing changed, the value is still at 6400.
I hope you could help me. Thanks