"Cannot start Omnisharp because Mono version >=3.10.0 is required"
When you installed it, you probably used
sudo apt-get install mono-completeIn my case, this installed Mono 3.2.8 which is evidently lower than 3.10.0. I couldn't manage to upgrade my Mono installation to a more recent version until I found this workaround:
sudo apt-get install mono-develThis will install the developer package which, as of yesterday, comes with Mono 4.0.1. This will replace your existing Mono 3.2.8 installation with the newest version and when you restart VS Code, you'll notice that the error is gone and everything seems to work perfectly. Likewise, executing a program will also no longer have TypeLoadExceptions.
I blogged about this in more detail here.
I still can't update my mono version using sudo apt-get install mono-devel until I follow the official website.
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EFecho "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.listsudo apt-get update