That error comes up when the system doesn't have a recovery partition on a system (on a UEFI system, it likely only has the UEFI boot partition, but not the "extra" recovery partition). If that is the case, bitlocker cannot launch any recovery options, therefore the only option is to boot from installation media and use the recovery options from there. Bitlocker encrypts the boot partition, and recovery is likely on the boot partition (thus bitlockered, thus the system cannot run recovery if bitlocker is not working properly because recovery is behind the broken / inaccessible bitlocker protection).
That's the root cause of not having any bitlocker recovery options on a system, anyway. They still exist in the recovery options on the installation media, though. This is why I tell people not to mess with the partitions that Windows tries to set up, though, unless they *really* know what they are doing. I would imagine Dell didn't ship the tablet in this state, but anything's possible (although it's more likely it's been rebuilt/reformatted at some point and reinstalled improperly, I don't ever rule out a broken image from the factory - it's just not likely).
