Please, I would like to know how to fix this problem in order to install Ubuntu 11.04 again.
[Error 30] Read-only file system:'/target/boot/vmlinuz-2.6.38-8-generic'
If Linux detects a problem on the harddrive, it will switch the filesystem to read only to prevent damage to the filesystem.
Since this is happening during install, I would assume something is wrong with the CD (ie. a bad ISO). You can find this out by running the 'check cd' option you get during boot. If this shows errors you need to re-download and re-burn the install disc.
If the installation disc turns out to be perfect it is likely to be a hardware problem. It could be your hard disc that is failing. Or if it is a desktop it could also be a faulty cable.