I experienced the same problem on my Acer Aspire 4720Z. As usual, the Acer support folks were not much help. They just send you the instructions to recover your system. They don't tell you how to get past the type mismatch error. I think this error message has something to do with the OS partition (partition 2) being corrupted. The way I got past the type mismatch error was to boot up using a WinPE CD then format partition 2 using diskpart. Here is a link from MS on how to create a WinPE CD. http://support.microsoft.com/kb/303891
Here are the steps to use diskpart. Insert the WinPE CD in your CD drive. Change your BIOS setting to use CD/DVD as the first boot option. Save your changes and boot up. Once your machine boots up with WinPE, at the prompt, type diskpart then hit enter. Enter the following commands and hit enter after each command is typed: select disk 0, select partition 2, format fs=ntfs quick. When all done, type exit then hit enter. Insert your Acer disk formatter then reboot the machine. Follow the instructions to format partition 2. When done, insert your Acer System Disc then reboot. Follow the prompts to recover your system. You will need the Acer Recovery discs. Follow the prompts. You will see a progress screen. Hope this helps!