How to Fix “OST is in Use and Cannot be Accessed” Error?

Tej Pratap Shukla ~DexterServer Administrator
Sometimes OST files might have errors like ‘the file username.ost is in use and cannot be accessed’. This article looks at some of the best ways to deal with this issue.

Microsoft Outlook and Exchange Server are used by most business organizations across the world. As both are very popular, users need to be aware of OST files used by Microsoft Outlook to store a replica of Exchange Server mailbox contents on the local machine. With the help of the OST file, it becomes easy for users to work in Outlook while offline. 

Yet sometimes, error messages are returned when a user tries to access their OST file. For example, “username . ost file is in use and cannot be accessed.” This error message states that the OS file that a user is trying to access is in use by another application. The reason behind such an error and how it can be resolved is explained here.

Why “OST is in use and cannot be accessed” Error Encountered?

If a user tries to go for the “Save and Send” service incorporated in Office applications, an Outlook error “the file xxxx  . ost is in use and cannot be accessed” is sometimes experienced. This error message generally states that the OST file of Outlook is in use by another program. Apart from this, there can be other reasons for this error:

  • There might be some synchronization problem between Outlook OST and related Exchange mailbox
  • Conflicts between some other program and Microsoft Outlook
  • Multiple users attempt to access the same OST file (mostly seen in networked systems)
  • Due to an unreliable or slow internet connection
  • If an unauthorized user tries to access the OST file, then also it might result in such error.
  • Another possible reason is processed, for example, UCMAPI.EXE, Office Communicator 2005 or 2007, LYNC,   etc running in the background.

Troubleshooting the “OST is in use and cannot be accessed” Issue

To identify the reasons behind this error, it’s time to use the various troubleshooting tricks discussed below:

Trick #1: Close Outlook & All Related Processes

First of all, a user needs to make sure that all Outlook related processes are not in a running state because they can also leave Outlook  . ost in an “in use” state. To do this, follow the steps mentioned below:

  • First of all, close the Microsoft Outlook application
  • After that, you have to open the Task Manager and go to the Processes tab
  • Then, you need to find the processes with name LYNC, Outlook, UCMAPI, or Communicator
  • Now, you need to choose all these processes and click on the End Task button to kill the processes.

Trick #2: Disable Exchange Cached Mode

To turn off Exchange cached mode, follow the steps mentioned below:

  • First of all, exit MS Outlook and go to Control Panel
  • After that, navigate to Mail >> Email Accounts >> Email
  • Here, you need to select the desired email id and click on the Change button
  • Then, simply uncheck the Use Cached Exchange Mode option
  • Now, click on the Next >> Finish button to complete the process

Trick #3: Run Inbox Repair Tool to Repair Corrupt OST File

Microsoft provides a free inbuilt utility named as scanpst.exe or Inbox Repair Tool to repair issues encountered in Outlook. It is a pre-installed tool in Outlook that is used to repair damaged OST and PST files, including all data items in it. To use this tool, follow the steps mentioned below:

  • To start the process, close Outlook application
  • Then, go to (C:) Drive -> Program Files -> Microsoft Office -> Office14 -> SCANPST
  • As you click on the SCANPST option, Microsoft Outlook Inbox Repair Tool Window will appear on your screen. Here, you need to click on the Browse button and select the OST file that you want to repair
  • After that, click on the Start button and scanpst.exe will scan the OST file and perform a consistency check on it
  • Next, a new window will appear that specifies the OST file location and all folders found in that file ( Do not forget to check "Make backup of scanned file before repairing" option. At last, click on the Repair button to start the OST file repair process).
  • Once the process has completed, a Repair complete message will be displayed on the screen. Just click on the OK button and terminate the process
  • This application is used to overcome only minor levels of issues related to the OST file. In the case of badly damaged OST files, scanpst.exe fails.

Trick #4: Via Professional Tool

If any of the above tricks are unable to fix this “OST is in use and cannot be accessed”, then it is clear that one needs to look for some professional solution. 

SysTools OST to PST Converter is one such type of application that a user can try to overcome all OST file related issues. It is designed to remove all types of corruptions from OST files in just a few simple clicks. Using this application, one can repair all data items stored in emails, contacts, tasks, etc. Moreover, the software is compatible to repair OST files with both minor and major level corruption. A user can use this application in any version of Microsoft Windows OS.


Microsoft Outlook is an amazing application with all required features to enhance a business. But no application is free from problems, same is the case with the Outlook OST file. One such commonly encountered error by the user is “OST is in use and cannot be accessed”. Thus, to access the Outlook  . ost file in a normal way, it is necessary to fix this error. Hence, the above post discusses various troubleshooting tricks to achieve this end goal.


Comments (1)

Kurt JohnsonTechnical Manager

Thank you for sharing this informative post Tej.

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