Try to reinstall the program in this case. Also you are saving the project or are you exporting the project, make sure that if you´re exporting it select a standard size and format. Also check the size of the files that you are adding into the project, each file is going to try to fit into the canvas, but if you have small size, black bars are going to appear.
If you continues having problems send the information to: https://www.nch.com.au/support/