I had the same problem. I fixed it by this.
Open a terminal, type this
Code:
mv ~/.config/chromium/Default ~/.config/chromium/Backup
Now run chromium, and it should work. Then close it, and type this in your terminal.
Code:
rm -rf ~/.config/chromium/Default
cp -R ~/.config/chromium/Backup ~/.config/chromium/Default
Then when you open it all of your preferences should be back, and everything should be good.
EDIT:
If you want an easier way and don't care about your bookmarks and preferences or anything, you could close it and type this.
Code:
rm -rf ~/.config/chromium/Default
Then when you open it you should be able to start from scratch.
Bookmarks