Canon 6d - shutter speed is being limited

[starcrazy8]

I shoot full manual 98% of the time. Recently, whenever I set up a shot (for example, f/2.8, 1/500th, ISO 320) I will press the shutter half way to focus and the camera will revert my shutter speed to 1/180th of a second and not let me shoot any faster.  I do not have any sort of external flash set up - there's nothing in the hotshoe at all.  I've checked all my settings and can't quite figure out why it won't let me shoot over 1/180th. I have a wedding to shoot tomorrow and I'm getting really frustrated.  Any help is appreciated!! 

[TCampbell]

That's the max flash sync speed for your camera. Your camera thinks you have a flash.

I'm wondering if you have anything in the hot-shoe. There is a tiny micro-switch (a little black button) hididng under one of the leaf springs in the hot shoe rail. That might be sticking.

You might want to go into the flash control menu and disable external flash -- see if that doesn't make a difference.

[ebiggs1]

You need to reset the camera.  Do a "Clear all settings" in the menu.  You have set something wrong.