Unable to insert the virtual optical

How to resolve below errors?

Unable to insert the virtual optical disk C:\Program Files\Oracle\VirtualBox\VBoxGuestAdditions.iso into the machine Ubantu.

Could not mount the media/drive 'C:\Program Files\Oracle\VirtualBox/VBoxGuestAdditions.iso' (VERR_PDM_MEDIA_LOCKED).

Result Code: E_FAIL (0x80004005) Component: ConsoleWrap Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed} Callee: IMachine {5047460a-265d-4538-b23e-ddba5fb84976}