Fixed Error “The file username.ost is in use and cannot be accessed” Manual Method

In Outlook, The Error “The file username.ost is in use and cannot be accessed” is Solved

Summary: An OST file is an Outlook data file that can cause errors such as"The file xxx.ost is in use and cannot be accessed." This can be fixed by using DataHelp Converter for OST to convert corrupted OST file to PST format. There are, however, a few troubleshooting methods you can use to resolve the Outlook error.


If Cached Exchange Mode is enabled in Microsoft Exchange, a replica of the server's mailboxes is created on the local machine with the.ost extension. This ‘cached mode improves Outlook performance by allowing users to work offline.



All changes made in the local mailbox cache (.OST) are synchronized with the server mailbox when the server comes back online. However, an Outlook user may occasionally encounter errors such as, due to a problem with the OSTfile.



‘Cannot access the fileC:users....username.ost because it is in use. Try again after closing any applications that are using this file. It's possible that you'll need to restart your computer.'

The Causes of the Error

The error can occur for a variety of reasons, but it most frequently occurs when a user tries to “Share” or “Save and Send” an MS Office file using programs like MS Word, PowerPoint, or Excel.

The error indicates that another program is using the Outlook OST file, and closing it may fix the problem. Most users, however, will have difficulty identifying the specific program or process that is causing the error. The error also advises the user to restart the computer, which usually fixes the problem.
However, another program does not have to be using the OST file. There could be a number of other reasons for the error, including:

Microsoft outlook and conflicting applications

Attempts by multiple users to access the same OST file (typically in the case of networked systems)

Slow internet connection or unreliable network connectivity

Access to the OST file without authorization

Background processes include Office Communicator 2005/2007, LYNC, UCMAPI.EXE, and others.

How to Fix MSOutlook Errors in 2019 and All Versions

The following are some methods for troubleshooting and resolving the “The file xxx.OST is in use and cannot be accessed” error:

Method1: Stop Using MS Outlook and other Related Programs.

Make sure that no more than one instance of Outlook is running on the same machine, and that no other related processes that require access to the OSTfile are running. The OST file may be marked as "in use" as a result of this. The steps are as follows:

Open TaskManager after closing Outlook.

Go to the"Processes" tab.

Look for processes named "Outlook," "LYNC," Communicator," or "UCMAPI" in the list.

One by one, select such processes and press the "End Task" button.

Then check to see if the problem has been resolved.

Method 2: DisableExchange Cached Mode

Turning off the "Cached Mode" is another way to solve the "OSTcan't be accessed" problem. Follow the steps below.

Open ControlPanel after quitting Outlook.

Go to Mail>Email Accounts> Email Accounts> Email Accounts> EmailAccounts> Email Accounts> Email

Choose your email address and then click the "Change" button.

“Use CachedExchange Mode...” is unchecked.

Select the Next option.

Finish by pressing the Finish button.

Even if the error hasn't been resolved, don't forget to enable Cached Mode.

Method3: Locate and Disable IncompatibleOutlook add-ins

Though add-ins are supposed to improve Outlook's functionality, they can sometimes cause problems, such as making an OST file inaccessible.

Disabling the problematic add-ins may thus resolve the issue, allowing you to access your Outlook account and OST file. You must start Outlook in Safe Mode to see if the error is caused by a faulty add-in. Follow the steps below.

Close Outlook and then presses Windows+R to open it again.

Press ‘Enter'after typing Outlook /safe.

Check if the error has been resolved by using Outlook normally.

If the problem has been resolved, restart Outlook in normal mode and disable add-ins one by one, looking for the error. This will allow you to remove the faulty add-in while keeping the non-faulty ones.

Method 4:Create an OST File from Scratch
You can try to recreate the file if the OST file is still inaccessible and the error hasn't been resolved. This can assist in the correction of minor OST file corruption issues.

In order to do so,

Close Outlook and navigate to the location of the OST file.

After that, rename the OST file extension to. bak.

If the OST filename is abc@xyz.com.ost, for example, rename it toabc@xyz.com.ost.bak.

Then go ahead and open Outlook. The OST file will be recreated, and the mailbox items will be synced.

If this doesn't work, you'll have no choice but to convert the data in the OST file to PST. PST stands for Personal Storage Table, and it is an Outlook data file that can be imported into any Outlook profile. The next method explains the procedure.

Method: 5 Convert OST to PST

There are two methods for converting OST to PST.

Using the Outlook Import/Export wizard manually

Using the OSTto PST Converter

Using the OutlookImport Export Wizard, convert OST to PST.

If you have access to Outlook, you can use the Outlook Import/Export wizard to convert an OST file to a PST file.

To import data into Outlook, go to File> Open> Import.

The ‘Important Export Wizard' will appear.

Click the next button after selecting ‘Export to a file.'

Select ‘Outlookdata file (.pst)' from the next screen and click ‘Next.'

Click on browse to select a location to save the converted file, then finish.

The OutlookImport/Export wizard may not work if the OST file is inaccessible. Use the OST to PST converter tool in this case.

DataHelp Converter Tool to converts OST to PST.

TheDataHelp Converter for OST makes converting an inaccessible OST to a PST a breeze. An Outlook user can easily export the mailbox in an OST file to PST using its intuitive graphical user interface and useful features, even if the file is orphaned or encrypted. It converts OSTto PST with 100% accuracy and data integrity.

This tool can help you avoid errors like "The file username. ost is in use and cannot be accessed" and other OST-related issues. You can use the demo version to scan and preview all of your OST mailbox components before saving them to a.pst file for free.

Additionally, you have the option of exporting OST mailbox items to other file formats. A Technician version is also available, which can directly export your OST mailbox to a Live Exchange server, Office 365 account, or Outlook profile.

Putting the pieces together

Through various troubleshooting methods, the guide will assist you in resolving "The file username.ost is in use and cannot be accessed" and making the OST file accessible. However, using an OST to PST converter tool like DataHelp Converter for OST is the best and most reliable way to fix the error and prevent further damage to the OST file.

However, you are free to try the troubleshooting methods at your leisure. If they fail, don't be afraid to fall back on this tried-and-true solution.