Probably because your C: drive is partitioned as FAT32, and you are using a version of DOS prior to 7.0, or your C: drive is partitioned as NTFS, and you are using any version of DOS. It can't read the drive, because it doesn't recognize the format.
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Re: How to create our bootable CD
Probably because your C: drive is partitioned as FAT32, and you are using a version of DOS prior to 7.0, or your C: drive is partitioned as NTFS, and you are using any version of DOS. It can't read the drive, because it doesn't recognize the format.