600EXII-RT stuck in FEL mode.

[clementlo]

Hi all, I am new here.  I got a Canon 5D Mark IV.  Today, I try to use my Flash, as soon as I plug my Flash into the Camera body,  I get "FEL"  and  I got a Lightning Bolt with a star on the corner.  And it lock out my camera, I can't get it off.  Can someone help me?  Many Thanks.  I try restting my camera setting, it won't help.

Is my Flash malfunctioning?  Please see attach picture.

[MikeSowsun]

Try resetting the flash settings. Mount the flash on the camera and use the camera's flash menu to clear all the flash settings. 

[clementlo]

Thanks, after searching for hours, I found my M-Fn button stuck pushed in!  I never use that button!  I have to try to pick that button back out and then exercies the button in and out couple times... now I free the button, but still sticky...  I just have to disable the button I guess.  I hardly use it.