MIne did it the other night too.
I have the same tv
It stuck on dynamic mode too after firmware upgrade.
Just do a factory reset of the tv.
Goto Menu support, Self Diagnosis, reset.
If it asks for a pin put in 0,0,0,0.
Let the tv restart and should be fixed.
I own a Samsung PN51E550D1FXZA and just did the online update through the tv. After the firmware update I am unable to change the picture mode from Dynamic to Standard or Movie. I'm also unable to switch the Speaker Settings from TV to External.
Has anyone had this problem and know how to fix it or how to downgrade the firmware to the previous version? Thanks for your help.