.ost error in Office 2016 (O365)

We are experiencing an issue with opening Outlook for one user account, when we set the account and try to log in we get the attached error message.

This happens on any PC (Have tried multiple PCs that the user has never logged into), have set up the account on my profile and still get the same error message. This user is using a roaming profile, but it does not include the Appdata\Local location. All other users are set up the same way and nobody else has this issue.

Other things I have tried:
  • Recreated profile (Cached mode on and off)
  • Checked permission on OST
  • Windows 7 and Windows 10 OS
  • Deleted and recreated roaming profile folder
  • /resetnavpane
  • Safe mode (Same error appears)
  • Removing profile from PC (removed reg keys and profile folder)
  • Compared Attributes in AD with a working account

Any ideas on where we should be looking next?
Daniel BourneAsked:
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Sandeep KumarAssociate ConsultantCommented:
Hello Danial,

Almost all possible things you already did which could be the reason for such error.

According to Microsoft, the main cause of this issue is a corrupted 'Navigation Pane' settings file, i.e., profilename.xml, where "profilename" is the name of your Outlook profile. All versions of Microsoft Outlook from 2003 to the newest Outlook 2016 may be affected by this.

Turn off compatibility mode in Outlook, PST or OST file could be corrupted. Reinstall MS Outlook and configure Outlook profile via auto method.

Further check it for working or not after that to restore your Outlook data from corrupt OST file. You can use Kernel for OST to PST converter tool for the recovery of OST emails. Visit: https://www.nucleustechnologies.com/ost-to-pst-converter.html to know about the tool.

Hope it will sort your issue.

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Brian BEE Topic Advisor, Independant Technology ProfessionalCommented:
You have done a good job troubleshooting all the usual stuff. You said you tried cache mode off. Did you still get the error then? That doesn't make any sense because you would not be using the OST at that point. I have seen this work:
- turn chance mode off
- delete the OST
- opening Outlook
- turn cache mode back
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