Trial routing is dirty routing that typically used for estimation. So, DRC violations are expected. But if they still exist after Nanorouting (I mean the same violations) you need to check that dirty routing is deleted by NanoRoute before performing actual global/detail phase. Use editDelete -type Signal to delete all signal wires before NanoRoute. Please notice that clock wires will be deleted too. You can deselect it from deletion by using editSelect/editDeselect commands.