This 'question' is more of a possible solution to others who were in the same scenario that I was stuck in for a few days.
I had a file that had been created after a failed software install, inside two folders which were owned by a special 'shared' user who cannot login - it's just a way to access network shares without my main account details.
I tried all the usual solutions, take ownership, third party programs, delete from command line - nothing was working... the file apparently didn't exist whenever I tried to delete it, and deleting folders gave permissions errors regardless of owner.