Welcome to troubleshooting performance issues - MS Outlook Performance Series - Part 6
One of my customer reported that he is facing issue with Outlook 2007 & Windows Vista environment, as he can't open the .pst files.
He get the following error: <sample>.pst file could not be opened. The file may not be compatible with this version of Outlook or it may be corrupted.
End of the research, we found the issue happens due to the mail file is in an encrypted folder.
To work around this problem, we need to make use of Inbox Repair Tool (Scanpst.exe) to repair the personal mail file.
Please find the following http://support.microsoft.com/kb/934545 which describes the issue, causes and its resolution in-detail.