Resolve Error: “The file username.ost is in use and cannot be accessed in Outlook”

Outlook offers “Exchange” settings to configure an account in MS Outlook. Exchange Server provides the facility to start the “Exchange cache mode” for making a replica of all mailboxes in your local machine. Outlook saves these mailboxes in .ost file. With OST files users can access their emails in offline mode and also it helps in increases the performance of Outlook. But sometimes there comes a situation when users face the error “The file username.ost is in use and cannot be accessed in Outlook“. After this, they are searching for a quick solution to resolve this error.

The instant solution to resolve this kind of error of MS Outlook user should try the method to convert OST to PST file. Through this method, users can transfer the important data from any corrupt OST to a working PST file.

All users can try the Free OST to PST Converter to instantly convert OST file and access the PST file inner without getting any kind of problem. For a quick demo of this tool download it from here:-


Reasons behind this error:-

  • While synchronization of files, some complications may erupt between Outlook OST and the respective interconnected Exchange mailbox.
  • Interlink within another program on one side and Microsoft Outlook on the other side.
  • If the internet connectivity is moderate, reckless, and continuous connection breakdown.
  • If various users try to retrieve or gain access to the same OST file.
  • Such error may also be notified if an uncertified user attempts to obtain the OST file.
  • If the user is operating any other application in the foreground like LYNC or Office Communicator, etc., then also such errors may evolve.

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

The strategy and tactics applied for solving the error :-

  1. First, quit Outlook on the system.
  2. Now, open the ‘Task Manager
  3. Then, select the ‘Processes‘ option.
  4. From the available options, Outlook, Communicator, and LYNC are selected.
  5. Now, choose the ‘End Task‘ tab.
  6. After that, Open the ‘Control Panel’ option.
  7. Click on the ‘Email Accounts’ tab.
  8. Now, press the email address option and double click on ‘Change‘.
  9. Then, move on to the “Use Cached Exchange Mode” option.
  10. Click on the ‘Next‘ option and then ultimately Click on ‘Finish‘.

Solution 2:- Remove Unusable Outlook Add-ins to resolve this OST file is in use and cannot be accessed

Malfunctioning add-ins lead to errors and also alters the working of Outlook. When getting any error like- “The file username.ost is in use and cannot be accessed in Outlook” it is highly recommended to access Outlook ‘Safe Mode’.

  • Close MS Outlook application then press Windows+R keys to open the “RUN” box
  • Now type Outlook /safe and press ‘Enter
  • Use Outlook in safe mode and check the is fixed or not.

If this method helps you then simply remove the corruption causing add-ins from Outlook.

Solution 3:- Resolve Error through ‘ScanOST.exe’

Microsoft Outlook has an incorporated tool called ‘ScanOST.exe‘ that authorizes users to fix the unwanted errors. ScanOST.exe tool can be a solution to resolve the error “The file username.ost is in use and cannot be accessed in Outlook“.

  • Firstly, Close Outlook and start the ‘ScanOST.exe‘ file.
  • Hit on the browse button and simply choose the respective OST files that are to be repaired.
  • Click on Start to proceed with the scanning process of OST file corruption errors.
  • Click on ‘Repair’ and simply repair your corrupt OST file.

Solution 4:- Convert OST to PST

There are two method available to Convert OST file workable PST file:-

To perform the the conversion process of OST file to PST manually user can try the Import/Export wizard.

  • Firstly Start MS Outlook
  • Click on File>> Open & Export>> Import/Export
  • And open the ‘Import and Export Wizard’ of Outlook in your machine.
  • Select the ‘Export to a file’ option and click on ‘Next’.
  • From the next screen select the option ‘Outlook data file (.pst)’ and click on ‘Next
  • Click on ‘Browse’ to select the location for saving the resulted PST file and click on ‘Finish’.

This utility can transfer the the data from OST file to PST. But in some cases, it doesn’t give the guaranteed results because of corruption error in OST file. So it is recommended for the user to go with an automated solution like eSoftTools OST to PST Converter Software.


By using this tool user can convert any type or any sized OST file without facing any kind of problem. Before purchasing this software user can try a free demo version this software. The demo version works same as the full version of this OST to PST Software and offers to Convert OST file with selective 25 items from per folder without any charges.

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