You should delete line 402 of the file Game Event Sheet.xml, you cannot have two triggered conditions at the same block, you can only combine 1 triggered condition with ticking conditions.
I don't know how you ended up with that, C2 usually prevents you from adding a second triggered condition. Maybe you modified the xml file with a text editor some time ago.
No, never edited any file like that. It just stopped opening the project. I tried deleting that line, still won't open, get another error: