Re: cannot mount /dev/lop0 (/cdrom/casper/filesystem. squashfs
Just chiming in with the same problem and what worked.
MD5 was good but trying to verify MD5 on the burnt CD failed.(Brasero) Not sure if it has something to do with the SATA controller as posted before or not, but using a USB stick worked fine.
If this error is indeed caused by multiple unique scenarios, I would think it would be easier to track down the code and insert a proper "Laymans" error message with maybe some suggestions for a fix. This would considerably cut down on the frustration for a new user and make the whole experience tolerable should something go wrong.
First impressions are everything, and printing out cryptic messages on a console screen would turn off all but the most determined. If Ubuntu has hopes of competing with the big boys, it needs to be on top of an issue like this, if only just a message on how to get further help. I'd be kinda embarrassed if I was trying to convert someone and this happened to them. I really hope this gets the attention it deserves.
Xubuntu 12.04LTS (Precise) 3.2.0-51-generic x86_64
Xfce 4 Desktop Environment - version 4.10.2 (Xfce 4.10)