As you can see from the log, the diskimage file is 549666608
bytes, but it only downloaded 2728096
bytes. That's why the extraction failed. Try running it again and make sure your internet connection is good.
06-03 02:36 DEBUG downloader: Download start filename=D:\ubuntu\disks\ubuntu-12.04.2-wubi-amd64.tar.xz,
url=http://releases.ubuntu.com/12.04.2/ubuntu-12.04.2-wubi-amd64.tar.xz,
basename=ubuntu-12.04.2-wubi-amd64.tar.xz, length=549666608, text=None
06-03 02:53 DEBUG downloader: download finished (read 2728096 bytes)
06-03 02:53 DEBUG TaskList: ### Finished download
06-03 02:53 DEBUG TaskList: ## Finished get_diskimage
06-03 02:53 DEBUG TaskList: ## Running extract_diskimage...
06-03 02:54 ERROR TaskList: Extraction failed with code: 2