Compiler Error CS1617
Invalid option ‘option’ for /langversion. Use ‘/langversion:?’ to list supported values.
For example
Invalid option ‘6’ for /langversion; must be ISO-1, ISO-2, 3, 4, 5 or Default
Solution
Right click on your project and select “Properties” from menu.
Select Build menu and, in the bottom, click on button “Advanced”.
In the next form you don’t have any voice for the field “Language Version”
Select “default”
Done
