For reasons not important here, I made an image from files and folders on a CD (not of the complete CD). The next time I tried to use ImgBurn, it tried to mount that drive but there was no CD present resulting in a Cancel, Continue, Retry error message. None worked and I had to abort ImgBurn, put a CD in the drive, and then start ImgBurn and finally change to a usable drive.
In this case, Cancel should do exactly that and let you select a new drive.
Jerry