This sounds much like an incomplete/corrupt ISO download. When that happens, it might boot but then fails randomly.
Please run "md5sum YOURFILE.iso" on the ISO file you downloaded and reply with the output. It should match the hash value listed here: http://releases.ubuntu.com/11.04/MD5SUMS
If running Mac OS X, the command should be something like "md5 YOURFILE.iso" in a Terminal window.
This sounds much like an incomplete/corrupt ISO download. When that happens, it might boot but then fails randomly.
Please run "md5sum YOURFILE.iso" on the ISO file you downloaded and reply with the output. It should match the hash value listed here: http:// releases. ubuntu. com/11. 04/MD5SUMS
If running Mac OS X, the command should be something like "md5 YOURFILE.iso" in a Terminal window.