The error certainly seems to suggest that there is a permissions issue.
Can you connect to the machines registry remotely from the console machine (using the Windows Registry editor)?
Can you connect to the machines root drive share from the console machine (i.e. C$ or IPC$)?
Can you remote manage the machine from the console?
Are you able to perform successful forward and reverse DNS lookups of the machine from the console?
If you are able to successfully perform all of the above actions, test by adding the machine to a new machine group, then specify machine specific credentials using the same credentials as those which you are currently logged into the console machine. Are you able to scan the machine group successfully?
If you are still unable to resolve the issue, it may be best to contact support directly so that we can obtain some log files for further analysis.