You may sue some manual method to change the format from .ost to .pst. Manual methods like Archive, Export, and Move can use used to fix OST to PST Conversion issue. Below is Export method guidelines:
1. First open the MS Outlook on your system.
2. Click on File tab. Select the “Import and Export” wizard or press ‘t’.
3. Click on the “Export to a file” from the list and then click on the Next button.
4. Then, select Personal File Folder (.pst) and again, click on Next button.
5. Click on the parent root and check the Include sub-folders option. After that, browse
and select the target folder. Click the Finish button
Also read:
http://recoveryandmanagement.com/rep...o-pst-outlook/