This issue may occur if the root password of the ESX/ESXi host has been changed after it was connected to vCenter Server.
To resolve the issue:
- Disconnect the host from vCenter Server. Do not remove it.
- Reconnect the host to vCenter Server. This should fail with an incorrect username/password error.
- Provide the correct root password and then try reconnecting the host to vCenter Server.
After the host is connected to vCenter Server, you should be able to refresh the datastore list successfully.