I also encountered this problem on a liveUsb installation, while trying to install bcmwl-kernel-source.
As a workaround (slightly different from Gary M's), I just corrected the /vmlinuz symbolic link to point to /cdrom/casper/vmlinuz.
The installation the finished successfully.
I also encountered this problem on a liveUsb installation, while trying to install bcmwl-kernel- source.
As a workaround (slightly different from Gary M's), I just corrected the /vmlinuz symbolic link to point to /cdrom/ casper/ vmlinuz.
The installation the finished successfully.