Sorry, but to use the FLR on Linux, you have to log on in a Linux virtual machine with GUI (and Flash enabled) and that virtual machine must be backed at least once.

Take a look at the VMware KB article: Logging in to the vSphere Data Protection Restore Client fails with the error: Cannot locate login c...

To resolve this issue, log in to a virtual machine where a backup job has been created and run to allow for file level restores.