http://social.bioware.com/forum/Dragon-Age-II/Dragon-Age-II-Demo-Technical-Support/XML-Error-line-1-column-40-6580716-1.html
Might help. First Google result,
EDIT: Okay the one person said they fixed it by creating a new Windows Admin account and installing the game again (it's DA2, but same error).
I'd try clicking running in admin mode. So right click on the install icon and click that. I had a similar problem installing Morrowind the other day.
I had to copy it to an external drive and run in admin mode to install it. Otherwise it kept giving me texture errors. Something screwy with Windows.