Unable to mount /dev/loop0 during install

The checksums (MD5) can be found on releases.ubuntu.com. I would suggest you do the following:

1. Check that the MD5 checksum of the ISO image you downloaded matches the one in the aforementioned link, by following these directions.
2. If that looks okay, boot the CD and press the Spacebar key when you see the keyboard icon in the bottom-center of the screen. Select your language, then the "Check CD for defects" boot option.

If neither of those produce any errors, please file a bug here, following these instructions to attach /casper.log to it.

There are two common culprits of this error:

1. The CD or disk you burnt to did not have enough space for the entire .iso.
2. The .iso you downloaded had a problem when downloading.

Make sure you at least do these simple checks when going to install:

1. Check that the size of the downloaded .iso isn't ridiculous (Ubuntu 10.x and 11.04 are each approximately 680 MB, if yours is only like 400 MB, you obviously have a problem).
2. Check the amount of free space on your CD or disk before you burn to it (and remember, DVDs have lots more space than a generic CD).

Did you check the download prior to burning?

You can use a program such as winMD5Sum in Windows to check md5sums

https://help.ubuntu.com/community/HowToMD5SUM#MD5SUM_on_Windows

The hashes you need to check against the downloaded iso can be found here https://help.ubuntu.com/community/UbuntuHashes

If you downloaded with a torrent then it should be checked as it downloads though.

If the hash check is ok then reboot with the cd and check it's integrity.

Press any key as the cd loads to see the cd menu