CS1617 Invalid option 'preview' for /langversion. Use '/langversion:?' to list supported values

[andydis]

Error when compiling:- CS1617 Invalid option 'preview' for /langversion. Use '/langversion:?' to list supported values

windows 10 1903 Visual studio 2017

Tried: installing all the .net SDK's / developer packs changing the projects target framework to 4.0 , 4.5 , 4.6.1 , 4.6.2 all same error

1>------ Build started: Project: SharpLocker, Configuration: Debug Any CPU ------ 1>CSC : error CS1617: Invalid option 'preview' for /langversion. Use '/langversion:?' to list supported values. ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========