Reinstalling game not possible to remove oil_upgrade

I assume you've gone into steam, rt-clicked ONI in your library, gone to properties, gone to the BETA tab, and swapped out of beta you would like to opt into: NONE - Opt out of all beta programs before you reinstalled?

Yes

I've narrowed the issue down to the installscript.vdr file in the 2015 folder. It can't be deleted or changed and that is causing the issue.

You might try this guide:

https://www.reddit.com/r/Steam/comments/611h5e/guide_how_to_download_older_versions_of_a_game_on/

on Reddit.

The folder will be located elsewhere if I recall, that version shouldn't get any updates after you download it if I recall, it probably will run fine through steam if you launch it via the executable in the folder.

Edited September 21, 2017 by eggsvbacon

Steam support resolved the issue with files being locked by remote access.

Status: Fixed.

Take out: try replicating the fault by uninstalling the game, and reinstalling the non-preview branch.