I had the same errors mentioned by the other posts in this thread. For me it came down to this note in the Bitlocker Management documentation:
If a remote desktop protocol (RDP) connection is active, the MBAM client doesn't start BitLocker Drive Encryption actions. Close all remote console connections and sign in to a console session with a domain user account. Then BitLocker Drive Encryption begins and the client uploads recovery keys and packages. If you sign in with a local user account, BitLocker Drive Encryption doesn't start.
Any machines I logged in to the console session with a domain user account started the encryption process without issue after the next compliance check (90 minutes in my environment). For spare or guest machines that aren't regularly used and had no one logged in, running "Manage-bde -on c:" via SCCM remotely also successfully encrypted and escrowed the recovery keys.