The cluster state is invalid. Migration cannot continue.

This is due to a component of Microsoft clustering being present without a cluster actually being defined. The primary reason for this error is having a shared disk that is active.
In the case of a shared disk being present, the disk needs to be reconfigured to be available to only one server. Per the Server Settings Migration wizard documentation .
SAN-based storage presents itself to servers as locally attached storage. If using SAN storage, detach the storage from the source server and attach it to the target server.
For more detailed error information, perform Dtrace on ServerMigration process.
During the Enterprise Vault Server Settings Migration wizard on a non-clustered server the following error is displayed.