I'm not sure if my file is corrupt or a technical issue but I've created single solid body of the car body but if I attempt to delete a face and re-convert it back it back into a solid, solidworks immediate gives me the error message 'The feature could not be created because it would produce self-intersecting geometry" 

To make sure its not an error on my part, I split line an area of the solid, copied that surface and attempt to knit it and convert back to a solid yet it still gives me this error. The only way that works is patch and fill but that's not a solution for me as I've still got a lot of work left in modifying the shape. 

Even turning it back into a surface via deleting a surface and attempting to knit any kind of surface to it will result in the same error message.