If you are using the SCANPST.exe utility from microsoft and it is returning you with this error message “Fatal Error: 80040900″.
Then, most likely the problem is that the PST file is larger than 2 gigs. You can use the new tool from Microsoft to fix the PST.Click here to download the Exchange 2000 Tool: PST2GB

There are also others non Microsoft software that help fix your corrupted PST file.

e.g. EasyRecovery – FileRepair