Debian install failing due to CDROM not being detected

You can mount manually in a shell window (Ctrl + Fnumber)

mount -t vfat /dev/sdb /cdrom

But, the option of warsong works fine. It seems like a UNetBootin-Win bug u_u

I got the same error message when booting from a second partition of my usb stick. Zorbax' solution helps here too, however you need to choose the correct partition. For my case it was

mount -t vfat /dev/sdb2 /cdrom

Acccording to Debian-faq

This might be a little problem on older versions of Windows, as many Windows image-burning programs use their own formats for CD images.

And Wiki-ubuntu

Win32DiskImager is particularly good for pre-release testing and new releases, when the standard tools like Unetbootin might not be ready

Maybe there are an issue with unetbootin on some windows distro . You can use an alternative like : win32diskimager or Refus recommaded by Ubuntu , or ImgBurn ...