Hi,
Check the "status" column of your replicated VM on both servers and see if you have any messages (something that says that your replication still in progress, or something similar).
Did you enabled Replica on your primary server Hyper-V settings? If you enable replica only on your replica server and not on your primary server, you will be able to do failover but won't be able to failback to your primary site.
If that doesn't work, can you show us the exact error message you are getting?
Thanks,
Eddie