When running ADPrep on Server 2003 from Server 2008 media you may get this error:
Error message: Error(110) while running C:WINDOWSsystem32LDIFde.exe The system cannot find the file specified.(0×80070002)
<error message has been trimmed>
Pausing your AV software will likely allow the command to complete successfully. If it isn’t your AV there is something else that has locked one of the files ADPrep is using…
ADPrep on 2008 R2 media is supposed to not suffer from this issue, but I haven’t tested this.