I had a similar problem; it wouldn't let me convert either, said I needed to clean the polys, which I did, and it let me convert but it messed up a part of my geometry because it split some vertices. I merged them again and again and told me to clean polys every time, so I finally had to go back in, delete the area around the distortion and add a plane the fit it. Worked after that, and I have no idea why. Sometimes I wish I had my own personal Maya Pro, just waiting for me to ask for help lol.
"We don't actually need to know that the main character has a past. All we need to know is that he has an objective and a lot of people are going to die and a lot of innocent inanimate objects are going to be destroyed and blown up before he can complete that objective."