Are you getting any pertinent errors in the ESXi or vCenter logs?
Is this happening for all VMs, both powered on and powered off?
can you try copying the file in CLI (SSH or Shell) by running the following command and tell me the result?
cp /vmfs/volumes/(datastore1)/file /vmfs/volumes/(datastore2)/filePlease mark my comment as the Correct Answer if this solution resolved your problem
In the client go to Configuration - Storage and right click the datastore and browse. It opens up a window and you can see the various vm folders. In the Right Window right-click the folder and you should see copy. For some reason you don't see it in the left pane login to upsers
Thanks for the replies. I figured out the issue and it was pretty simple - the host was in maintenance mode, once this was exited all was ok.
It didn't help that I was looking for problems as we'd just had an issue with the raid controller and drivers/firmware but the strange behaviour didn't help either.
Sometimes when I performed a copy the destination folder was deleted (I think only when it was empty). Other times there was no response at all in vCenter to the copy.
Plus the error messages suggest a different issue. The hostd log said about maintenance mode, not sure why the errors in vCenter / ESXi wouldn't say the same?