The roswell beta installer will exit if a moutnpoint in the target /etc/fstab is incorrect, or non-existant. In the case of this test, /dev/hda6 at /mnt/test was defined as reiserfs, and actually existed as ext3. Anaconda exited with the message that the partition was unformatted or inaccessable. The only option was to exit the installer. This is less than intuitive, I think, and the option should be give to go back or format the partiion before the installer exits.
On upgrades we are very picky because we do not want to inadvertantly upgrade the wrong installation, or a misconfigured one, as this case was. That can lead to bigger problems. We notify the user of a problem so they can rectify it before we attempt the upgrade process.