What do Prescan Errors Mean?
Here is a great post on what prescan.exe errors really mean when encountered during their run prior to MOSS upgrade on an SPS 2003 site.
https://blogs.technet.com/wbaer/archive/2006/12/22/prescan-errors-what-they-mean.aspx
https://blogs.technet.com/wbaer/archive/2006/05/09/427831.aspx