Won't complete repair/update

Went to launch the game and was told it needed repairing, when repairing it stops at 80% and says it cannot create a file? The help button told me to clear cache, so I've done that but still having the same issue, says permissions issue and cannot create file... I was literally playing last night with no issues?
I've never ran any mods etc, just base game and a couple expansion packs 😊