Acronis True Image 2012 fails to back-up to a hard drive or a disc

I am using a trial version of ATIH 2012 and I have also used ATIH 2011 and when I attempt to make a back up disk image I am having the program shut the pc down during the process. This happens about 3/4ths of the time. It occurs whether writing to a hard drive or a dvd however when making an image to a dvd the sucess rate is much higher. This is on windows xp pro with sp3 and a clean install.