1. Right click installed OS and click "setting"
2. "Hardware" → "CD/DVD", "Floppy" remove
3. "Hardware" → "CD/DVD", "Floppy" creation
3-1. "Connection" of "CD/DVD" set equal to previous settings
3-2. "Connection" of "Floppy" set "Auto detect"
4. "Options" → "Guest Isolation" set two all checked