We are having an increase in the number of corrupt ost files with our users who are using the Outlook client in cached mode. We are currently running Exchange Server 2003 SP2 and Outlook 2007 SP2. We were running Office 2003 and upgraded to Office 2007 in August of 2009. Everything was working great until the beginning of December 2009. We started receiving help desk calls about users being unable to access their mailboxes via the Outlook client. They were receiving the error "the file C:\Documents and Settings\<username>\Local Settings\Application Data\Microsoft\Outlook\outlook.ost is not a personal folders file."
The frequency has been increasing over the past several months (over 100 trouble tickets with only 400 users located in this office) with no real pattern and we are unable to find a true fix. We have found many articles on the Inbox repair tool, and it will work sometimes, but not always...and never permanently. Needless to say, users are becoming frustrated. As a quick fix, we have been deleting the corrupted ost file and letting Outlook recreate it, but we would really like to find out why it is happening. What is even more frustrating is that we may fix one user’s ost, only to have it corrupted the next day or worse yet, several hours later. Some mailboxes are over 2GB which we have read can lead to corruption, but most are only 100MB to 500MB in size. Has anyone heard of anything similar to this or about anyone else that has been experiencing this issue? Are there any service packs or hotfixes that anyone is aware of that might have caused it? Any help is greatly appreciated.