The "Restore From Manifest" option is not available when there are no savepoints in the repository.
At this time there are 2 options to resolve this issue.
You can create and run a backup task. (For a quick backup, the VM that is backed up can be a blank VM.) This will create the savepoint necessary to allow you to access the restore from manifest option.
If you are unable to create and run a backup task or do not have the time for a backup, please perform the following.
Once the repository has been added you will be able to select the imported savepoint and proceed to the restore wizard.
To add an existing repository to a new vRanger instance, please view SOL96165.
You can also import an existing repository with the script as described in the communities thread: http://communities.quest.com/thread/10839 . This script will also allow you to create a custom repository with existing savepoints. For example you can copy savepoints from different repositories into the new repository and execute the script. The script will add the savepoints into vRanger's db which will create a savepoint grid. This will allow you to run a standard restore from the savepoint grid.