Upgrading Vista Home Premium to Ultimate

Hi,
I'm trying to upgrade an Acer Aspire 5920G from Vista Home Premium to Ultimate - something I thought would be an easy task. Unfortunately the upgrade fails on a Intel driver file - iastor.sys.

It says iastor.sys is missing or corrupted. From what I can see its actually the wrong (older) version.

Acer Support in Australia have been no help. They said no one else had had the same problem (a simple Google showed this to be false) and then palmed me off to some other company who wanted to charge me for support.

So does anyone have any informaion on :
1. This iastor.sys driver problem with upgrading
2. Any other tips / hints for upgrading an Acer laptop from Home to Ultimate

Regards
Michael