Microsoft has the following KB about a relatively infrequent crash that can happen during the SBS OS setup:
From the KB:
 110318.160407.0793: TaskManagement: In TaskScheduler.RunTasks(): The "ConfigureSharePointTask" Task threw an Exception during the Run() call:Microsoft.WindowsServerSolutions.Common.IWorker.IISConfig.IISConfigException: IIS Server Administration threw an exception. See inner exception for details. ---> System.IO.FileLoadException: Filename: \\?\C:\Windows\system32\inetsrv\config\applicationHost.config
Error: Cannot commit configuration changes because the file has changed on disk (emphasis ours)
We _have_ seen this error on systems we were installing while working with the OS prior to RTM. So far, we have not seen the problem on any of the servers we have installed using the RTM bits.
The only resolution at this point is to contact Microsoft Support via the provided link in the KB. Note that the current system is call-back based. Keep this in mind when quoting on migrating SBS between versions.
MIGRATION NOTE: It is _always_ important to take a full backup plus a System State backup _before_ making any changes to a source SBS when migrating to a new version of SBS. Without a good backup it is very difficult to step back if something goes wrong during the migration.
Please look into Jeff Middleton’s Swing Migration method if there is an absolute need for a fall back just in case something fails. Jeff’s method provides fall back while the Microsoft Method is committed once the mailbox move has been initiated.
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book