Help! How to delete single floor tile?

Hi! I have been having a similar problem, only it's to do with a rounded floor section. I have managed to narrow it down to the 3 and a half floor tiles which are bugging but I can't seem to get rid of them! I have tried everything I can think of - repairing game, restarting computer, bulldozing lot, moving lot, installing another lot, even just using the delete tool. Nothing works! I can't build over it or around it; dialogue boxes saying "Failed to compute cost" or "Invalid rounded piece intersection". Has anyone had the same problem and has a solution that doesn't involve deleting all my files and losing everything?