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Fix “The file username.ost is in use and cannot be accessed” in Outlook 2016

Updated On - September 25, 2022 by Henry Bray |

Reading Time: 4 minutes

While visiting Microsoft’s support forum, we found that a number of users have reported the “The file username.ost is in use and cannot be accessed” error. Actually, an OST file is stored on your device, which is a duplicate copy of your mailboxes on the MS Exchange server.

Basically, due to the issues with your OST files, the mentioned error occurs. This post is going to provide a clear concept about why the error occurs and what the possible solutions are to fix this error in Outlook 2016. Stay with us on this post and keep reading.

Reasons why the error The file username.ost is in use and cannot be accessed occurs:

The glitch can happen for a variety of reasons, but it most frequently occurs whenever a user attempts to share, save, or send an MS Office document using programs like MS Word, PowerPoint, Excel, and so forth.

Related Post: How to Import OST file into MS Outlook

The error means that yet another process is using the Outlook OST file, and trying to close it may fix the situation. Many users, even so, will struggle to identify the specific software or procedure that is causing the error. The error also advises the user to perform a simple restart of the device, which generally fixes the problem.

However, there may be a number of other causes for the error, including such as:

  • There may be a connectivity problem between both the OST and the corresponding Exchange inbox.
  • MS Outlook conflicts with other functionalities.
  • Attempts by numerous users to access the relatively similar OST file
  • Inadequate internet integration
  • Access permission to the OST file was not allowed.

Some effective fixes to solve the error “The file username .ost (format) is in use and can’t be accessed” in Outlook 2016.

In this main section, we will be discussing some methods that users can use to resolve this error and make OST data accessible for use. Basically, manual methods do not guarantee for the complete repair of the error that relates to the OST file. However, we believe you must try out these procedures before applying any professional solutions.

Run your Outlook in safe mode

This might be the most relevant and common fix that users can attempt to repair the error. It’ll just deactivate the defective Outlook add-ins or extensions that are causing problems with the Outlook functionality and its statistics. Therefore, execute your Outlook in the ‘safe mode’ and afterwards enter “outlook.exe/safe” into the empty command field (To execute the run functionality, tab Windows + R. You may consider it as a shortcut key.) wizard and simply tapping “OK”.

Fix The file username.ost is in use and cannot be accessed

Afterward, in your Outlook program, go over to “Options” and select “Add-ins.” Select the “Go” option. Pick the add-ins that you believe are fundamentally flawed and then tap the “Remove” choice.

Deactivate the cached mode of Exchange

The “Cached Exchange Mode” enables MS Outlook users to collaborate offline. The above error can sometimes be resolved by partially or completely deactivating this function. Follow the instructions underneath to deactivate “Cached Exchange Mode.”

  • Just after ending all MS Outlook functionality, navigate to “Control Panel.”
  • Then, in the Control Panel, select “Mail,” and a new dialog box will automatically appear.
  • Then choose “Email Accounts” from the opened dialog box, followed by “Email.”
  • Choose the email account that is linked to Outlook and afterwards tap “Change“.

Manual Ways to Repair The file username.ost is in use and cannot be accessed

  • Lastly, uncheck “Cached Exchange Mode” and click “Next” and then “Finish.”

Exit Outlook and end all relevant programs

Check that no multiple versions of Outlook are running on the same device and that no other related processes have access to the OST file.It can result in the OST file being labeled as “in use.” The stages are described.

  • Shut down Outlook and launch the “Task Manager“.
  • Choose the “Processes” icon.
  • Take a glance at processes named “Outlook“, “LYNC”, “Communicator”, or “UCMAPI” in the lineup.Step by step guide to repair 'The file username.ost is in use and cannot be accessed'
  • Select this kind of mechanism and tap the “End Task” icon individually.

Fix your faulty OST file with scanOST

If all of the preceding methods mess up, then maybe the OST data file gets corrupted. Users could indeed fix the data files for MS Outlook editions lower than or equal to 2007 using the unlimited (free) default utility scanOST.exe.

It is a major constraint as the latest Outlook editions have been released, but you can use the scanPST.exe software to repair.ost files in updated models of MS Outlook. Find the scanning process of scanOST as follows:

1. First, locate the scanOST tool in your device’s directory. If you are unaware of its location, then see the image as follows.

Easy Methods to repair The file username.ost is in use and cannot be accessed

2. Then, start the built-in tool. This has classified the individual’s Outlook profiles; select the OST data file repair profile.

3. After that, for the OST error checking, pick the files or folders of the OST file.

4. Then specify the “Repair Errors” checkbox and, afterwards, tap the “Begin Scan” button.

5. The scanning will proceed and, when finished, will display a factual notice stating that the scan has been finished.

However, if you miss your crucial data during the OST repair process or as a result of OST corruption, you can use the Regain OST Recovery software to recover your lost OST files.

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Author: Henry Bray

Henry Bray is a young technologist and content a Content Writer at Regain Software, loves to write about MS Outlook, MS Exchange Server, Office 365, Mozilla Thunderbird and many more email applications.

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