mkdir /cdrom
Note : If you got problems making the directory /cdrom, disable the CD-rom player in BIOS or disconnect the cable
Mount the USB as if it is a CD-ROM:
mount -t vfat /dev/sdb1 /cdrom
Where sdb1 is your USB device.
You could carry on installation now
Another layman solution was :
when the Window shows CDROM couldn’t be mounted ,
- Unplug your USB from system and re insert it
- wait for mount/ detection (usb LED glow)
- Hit Continue