If you wish to use DVD-RW media with Image for DOS, Image for Linux, or Image for Windows, the media must be either brand new, fully blanked, or formatted before each use. To be "fully blanked" means to be completely overwritten. This must be done using a third-party application such as Nero (in which case it would be the "Full-erase rewritable disc" option). Using a "quick erase" function will not work.
This requirement does not apply to CD-RW or DVD+RW. That is, Image for DOS, Image for Linux, and Image for Windows can overwrite CD-RW and DVD+RW discs natively.