Error: Cannot assign a drive letter to a partition from the image archive.

This error message is mentiioned in a few earlier posts. I have tried the suggestions in those posts to no avail. I created a full backup using Acronis True Image 8.0 about 10 years ago, the backup occupied 5 DVDs.Today I attempted to explore one of the backup files using the same version of Acronis as I created it with but I get Cannot assign a drive letter to a partition from the image archive.