1 parallel subtasks failed during execution.
Unable to connect to the VMM database because of a general database failure.
SQL error code: 547
Ensure that the SQL Server is running and configured correctly, then try the operation again.
We have received this error while removing a Hyper-v cluster out of VMM 2012 R2. Even trying to reinstall VMM agent fails manually. Trying both Remove-SCVMHost and Remove-SCVMHostCluster with -Force also failed miserably!
I have found a good article that takes you through these steps of removing hosts/cluster from the DB end, just make sure you have a backup before you start.
You can find the article here.