The File “username.ost is in use and cannot be accessed”

OST to PST Converter /February 05, 2025

Summary

Users working on Outlook and OST files often experience the “username.ost is in use and cannot be accessed” which is caused by different issues. It is necessary to analyze & fix the error to regain data accessibility, which we will discuss in this article below. However, to avoid data loss from OSt file corruption, we suggest you back up useful data using an advanced Goldytools OST to PST Converter that allows easy transitions.

Introduction

OST files are a very compatible option for Outlook users as it allows you to work in Offline mode without being connected to the servers. You can create a copy of your Exchange or IMAP Server locally and work on it, and after reconnection, the data will be automatically updated. However, an OST file sometimes throws multiple errors, which prohibits you from accessing the data file and may also damage the file completely. There can be numerous errors that can cause data inaccessibility, where “username.ost is in use and cannot be accessed” errors are also one of a kind.

In this blog, we will help you to understand the circumstances when this error can hit your OST file and why this issue occurs, along with possible ways to fix OST errors.

Reasons for “username.ost is in use and cannot be accessed” error

Due to technical failures or drawbacks, OST file throws accessibility errors as the file can attain corruption due to small negligence in system compatibility. Organizations carry their crucial data in OST files, and inaccessibility can cause severe losses in the business. So, to fix the OST error, you first need to identify the root causes behind “username.ost is in use and cannot be accessed” error:

  • OST file corruption: It is one of the most common causes for data loss which can be derived from multiple reasons like server failures, virus infusions, improper shutdowns etc.
  • Issue with Server: OST file is connected to Exchange or IMAP Server but if there is an synchronization error then it can damage your oST file.
  • Bad application: Installing unauthorized softwares & applications on your system can bring severe corruption & can damage the OST file.
  • Mailbox size: OST files keep updating automatically after reconnection with Exchange Server but if the mailbox gets big, it can become corrupted or damaged.

Ways to fix “username.ost is in use and cannot be accessed” error

It is very important to protect valuable data in an OST file from corruption, as it will lead to business downtime. Managing the above-mentioned precautions can help you to prevent OST file errors, but the chances of errors are still active. If your OST file has become inaccessible, then you need to fix the OST error immediately.

  1. Close application running in background

The error says that the OST file is in use then you must check if it is running in the background. It is crucial to check whether your OST file is not opened in the backup process or antivirus check. You need to disable if any of them keeping your OST file opened by following below steps:

  • Click on Start and search type Virus & threat protection.
  • Click on Virus & threat protection setting, go to Manage setting and click on the turn Off Real-time protection.
  • Restart the Outlook application and check if the error is resolved or not.
  1. Create a new OST file

Facing OST file accessibility issues then, it is more feasible to remove the old OST file and create a new one. Follow the steps to recreate a new OST file mentioned below:

  • Find the OST file in your system storage.
  • Usually the default location for OST file is – C:\Users\AppData\Local\Microsoft\Outlook.
  • Once you locate the damaged OST file and delete it.
  • Now, Outlook will automatically create the new OST file.
  • Restart the Outlook application
  1. Remove add-ins from Outlook

Microsoft Outlook consists of various add-ins which help in the functionality. But these add-ins can work the other way round and can cause damage & interruptions in the business. You can try by removing add-ins and then re-add them by following the methods mentioned below:

  • Launch Outlook application.
  • Go to Files>Options>Add-ins.
  • Select the COM Add-ins option.
  • You can deselect the add-ins you want to remove from the list.
  • Now, restart Outlook and see if it has fix OST error or not.

Conclusion

Microsoft Outlook allows a smooth flow of data on a daily basis and saves the data in an OST file but it is not accessible sometimes. In the above blog, we have discussed about the “username.ost is in use and cannot be accessed” error along with effective ways to fix it.
However, the most productive practice to protect your OST file data is to back up & save it in a PST file. So, we suggest you use Goldytools OST to PST Converter tool that helps to perform easy export from OST to PST.

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