So you are using Wubi to install Ubuntu inside Windows XP, is that correct?
First, be sure to fully defragment Windows before installing Ubuntu with Wubi. It helps to prevent problems like this.
Second, when you boot the Ubuntu live CD, choose the option "check disc for defects". This will take a minute or 2 to run. If it reports errors, then the disc is bad.
If you still have problems, try reading through the Wubi guide, especially the troubleshooting section about how to create a virtual disc in Windows:
Remember, according to Wubi's developer, Wubi is only meant to try out Ubuntu. It is not recommended for long term installations.
Agostino: Wubi actually wasn’t designed to do long-term installations. The main aim was really to let people try out Ubuntu with confidence. Normally, users that start with Wubi tend to upgrade to a full installation to a dedicated partition at the next release cycle.
If you plan to continue with Ubuntu, perhaps it is time to partition your hard drive and install Ubuntu the real way. See these 2 websites to get started with Ubuntu properly:
And welcome to the LQ forums!