I often get an error saying the .ost file is corrupt and I need to run SCANPST to make repairs. I'm connected to exchange using Outlook / Office 2007 Pro. I have a large email account in exchange so I believe the .ost file is justified growing to 3.2G. It's a laptop using Outlook in cached mode, since it's a laptop I can't turn off cache mode.  

To fix the problem I delete the .ost file in the profile, when I open Outlook for the first time it acts as if its never been connected to the server and begins updating the email files and folders. Once updated works fine for a week or so.

How do I determine what is causing the .ost file to corrupt.

There can be many reasons for OST file corruption. To know them in detail, go through this post  - http://www.techtricksworld.com/reasons-responsible-for-outlook-ost-corruption/

There are many reasons that will make your Exchange offline folder  (.ost) file corrupted or damaged. Here is a good explanation of this issue:

http://www.datanumen.com/exchange-recovery/corrupt-ost.htm

 Hello Oliver,

.OST file growing size is the one of the main reasons for corruption. I would recommend you to check the real size of your Exchange mailbox. If it exceeds 12 GB on server, then it is obvious that your .OST file will grow up to that size or even beyond, which can lead to noticable performance degradation and finally to corruption.

You can try the following. Create a new offline file and monitor it's size growing. It takes time until your Exchange mailbox is fully in sync. Depending on size and bandwith it can take hours.

If you find that too large file could be the issue, please read this article

I would like to suggest you to use of The Outlook .OST to .PST converter software, as it is clear from its title, can open Outlook files in OST format and convert this information into PST files, accessible offline. This software is free to try so users may evaluate how it works before buying OST2PST Kit.
For more information: http://www.ost2pstkit.com/#!/home

• Marked as answer by OliverHic 20 hours 38 minutes ago

Your OST file is corrupted that's why you are unable to access your data. Use Kernel for OST to PST Conversion Tool for the recovery of your OST file instantly.