VirtualBox won’t run win10: Failed to open a session for the virtual machine w10. Result Code: NS_ERROR_FAILURE (0x80004005)

VirtualBox Version: 6.1.22 r144080 (Qt5.6.3)

Host Operating System: MacOS BigSur

I came across exactly same issue, where clicking on add to choose image was crashing the dialog. This issue persists in the latest version of Virtual Box for Mac.

I could figure out couple of ways to avoid clicking on Add button to choose image.

First Option:

Steps:

1. Click on Settings to open settings window for your VM.
2. Choose Storage
3. Select Empty disc and choose Disk image by clicking small disc icon in the Attributes section. Please follow the image to have visual instructions.

Second Option:

Steps:

1. Click on VM’s Normal start
2. Once you get the option to choose image, simply cancel the dialog.

3. Now click on the small disc icon in the bottom of VM’s dialog to choose the image.

Hope this helps. Feel free to comment if you find this post useful.