Question: Unable to edit DC formula's in my own game.

As the title says I am unable to change the DC formula's on spells in my own game. Whenever I try to change a DC formula it shows a general prohibition sign and blocks me from editing. Is this a setting I need to change after the new update of VVT or something.

I am running vanilla build into the VTT, DND 5e with no add-ons. I have been running this game for close to 4 years and not had problems with being blocked from editing something before.

Any help would be great.