When you use scanpst to scan and repair your corrupt PST file, you can get following error message:

Fatal Error: 80040818

Precise Explanation:

For Outlook 2002 and earlier versions, PST file uses the old ANSI format, which has a 2GB size limit. Since Outlook 2003, a new PST format called Unicode format is used instead,  eliminating the 2GB size restriction. It is possible that your PST file is in old ANSI format, and it has reached the 2GB size limit, that is the reason why scanpst cannot fix it. You can use DataNumen Outlook Repair to convert the PST file from ANSI format to UNICODE format to solve this problem.