Hi, can you please explain what exactly you are doing here? Are you using the 3ds Max-native "viewport selection" option, or the Corona one? If you are not sure, can you please share a screenshot showing where exactly you are enabling this option?
Also, are you composing the final image with the black frame in Photoshop or some other 3rd editor, or are you doing all of this inside 3ds Max using the Corona VFB?
The more information you can provide about what exactly you are doing and what is happening, the better.
Thank you in advance for the details.