How To Fix “Cannot Start Microsoft Outlook. Unable To Open Outlook Window” Error

Advanced in Tech & Business

How To Fix “Cannot Start Microsoft Outlook. Unable To Open Outlook Window” Error

Microsoft Outlook is a perfect app for sending and receiving emails and managing other personal data. But sometimes Outlook doesn’t open and gives the “Cannot start Microsoft Outlook…” error message.

It may seem daunting, but there’s no need to panic. You can easily fix this from your home by using the methods in this article.

Causes for Cannot Start Microsoft Outlook Error

There are many probable causes for this issue, and different messages accompany the “Cannot start Microsoft Outlook” error in individual cases. Some of the usual reasons include:

  • Conflicts due to Add-ins.
  • Corrupted Navigation Pane XML file.
  • Corrupted data files or profiles.
  • Outlook running in compatibility mode.
  • Third-party interference.

Fixes for Cannot Start Microsoft Outlook Error

Depending on the cause of the error, there are several possible solutions. First, restart your computer and check if the error persists. If it does, move on to the fixes below:

Open in Safe Mode and Disable Add-ins

In many cases, this error occurs due to conflicts with Outlook Add-ins. You can check this easily by opening MS Outlook in safe mode. To do so:

  1. Open the Run command (Win + R).
  2. Type outlook /safe and press Enter.
  3. Choose your profile and click Ok.
  4. Enter password if prompted.

If Outlook doesn’t open, then some other causes are responsible. So, move on to the subsequent solution. 

If you can successfully open Outlook, disable all Add-ins by following the steps below:

  1. Go to File Options Add-ins.
  2. Look for Manage on the lower part of the tab.
  3. Set it to COM Add-ins and click Go.
  4. Uncheck all options and hit Ok.

Restart Outlook in normal mode. Then re-enable an add-in and restart again. Do this for all options to determine the culprit. Disabling the responsible add-ins should fix this issue.

Reset Navigation Pane

Corruption of the Navigation Pane’s XML file is also another reason for Microsoft Outlook failing to start. The error message should also mention “invalid XML” in such cases.

You can fix this issue by resetting the file. Here’s how you can do so:

  1. Open the Run dialog box.
  2. Type outlook /resetnavpane and press Enter.

Do this for all computers if you have more than one.

Repair PST Data File

There are many cases when the Outlook data files get corrupted and cause this error. The solution is to repair the files. Fortunately, Outlook includes a program to do just that.

You can use either POP3 or IMAP to receive messages. While using IMAP, Outlook uses a .ost file to store a synchronized copy of the data on your local drive. So, you can simply delete the file as Outlook will recreate another one during the next login.

If you use POP3, syncing is impossible, and Outlook will save all data on a local drive as a .pst data file. You’ll need to repair it if you don’t want to lose any information. To do so,

  1. Go to your Outlook folder.
  2. On windows, the path is something like C:Program Files (x86)Microsoft OfficerootOffice16 or C:Program Files (x86)Microsoft OfficeOffice15.
  3. Double-click on SCANPST.EXE to open it.
  4. Click Browse, and navigate to and select the .pst data file.
  5. Select Start to initiate the scan.
  6. After scanning, choose Repair.

If you want to know more about this process and what to do if you couldn’t recover all data, visit our article on How to Repair Outlook Data with the SCANPST.EXE tool.

On Mac, data files have the .olm extension instead of .pst and you need to use third-party tools to repair these files.

Delete OST Data File

As we mentioned in the previous method, you can delete the .ost data file. You can also delete the .pst file if you no longer need the data, but we recommend repairing it first, just in case. To delete the .ostdata file,

  1. Open the Run command and enter control. It will direct you to the Control Panel.
  2. Go to Mail or User Accounts Mail.
  3. Click on Data Files.
  4. Select the .ost data file and click Remove.
  5. Go to the E-mail tab and delete the corresponding email account.

Open MS Outlook and add the deleted account. It will recreate a .ost file by syncing from the server.

You can also delete the .ost file on Mac from Finder > Applications > Microsoft Office > Data Files.

Create New Profile

You can also try creating a new profile to check if the previous one has become corrupt. To do so,

On Windows:

  1. Open the Control Panel and go to Mail or User Accounts Mail.
  2. Click Show Profiles.
  3. Select Add, type a new profile name, and hit Ok.
  4. Follow the on-screen instructions to create the profile.
  5. In the Mail window, check Prompt for a profile to be used and click Ok.

On Mac:

  1. Open Finder and select the Go menu.
  2. Click Applications and go to the Microsoft Outlook app.
  3. Right-click on it and choose Show Package Contents.
  4. Go to Contents Shared support Outlook Profile Manager.outlook profile manager
  5. Click on the + icon and enter the new profile name.
  6. Right-click on the profile and choose Set Default.

If you can log in to the new profile in Outlook, the precious one has some errors. Back up the data from the old profile and remove it in such cases.

Check Compatibility Mode

If Outlook is running in compatibility mode for old OS, it won’t work properly in newer versions. So, disable compatibility mode and check if this resolves the error. To do so,

  1. Navigate to your Outlook folder and locate outlook.exe.
  2. Right-click on it and select Properties.
  3. Go to the Compatibility tab and uncheck Run this program in compatibility mode for.
  4. Click Apply and Ok.

Perform Clean Boot

Third-party applications are also known to mess with Microsoft Outlook, causing this error. A well-known offender is the Skype for Business application.

Boot your PC in safe mode to check if there’s any interference due to third-party processes. If no error occurs in safe boot, restart your computer in normal mode and perform a clean boot to isolate the culprit. Then you can repair or uninstall them. 

Repair / Reinstall Office

Another solution you can try is to repair or reinstall Microsoft Office. We recommend this solution especially if other Office components also show errors. Here’s how you can do so:

  1. Enter appwiz.cpl on the Run dialog box.
  2. Locate and click on Microsoft Office.
  3. To repair the application,
    • Select Repair or Change
    • Follow the on-screen instructions.
  4. To reinstall,

Also, make sure to reinstall it using an administrator account.

Update OS & Device Drivers

Outdated Operating Systems or Device Drivers can cause many system and application problems. Sometimes Outlook may fail to start due to issues with the system itself. 

We recommend updating them to the latest versions to troubleshoot the underlying bugs when you encounter this error.

Recovery Assistant for Microsoft 365

Microsoft provides a recovery assistant for Microsoft 365 to troubleshoot the Outlook not starting error. Download the file and run it if you encounter this problem in Microsoft 365.

Disable Cached Exchange Mode

If an Office 365 account has two or more Microsoft Exchange accounts, this error may happen in a few cases. To fix this issue, you need to disable Cached Exchange Mode in all but one account. Here’s how you can do so:

  1. Open Control Panel and head over to Mail or User Accounts Mail.
  2. Choose Email Accounts.
  3. Double-click on an account.
  4. Uncheck Use Cached Exchange Mode and hit Next Finish.

Increase MAPI Session Limit

By default, Microsoft Exchange limits MAPI sessions to 40 clients. If you exceed this limit, you will get the message “Cannot start Microsoft Outlook…The attempt to log on to Microsoft Exchange Has failed”.

Increasing the MAPI session limit should fix the issue. To do so,

  1. Connect to the Exchange Online PowerShell.
  2. Enter the command New-ThrottlingPolicy -Name <New Policy Name> -RCAMaxConcurrency 100 -ThrottlingPolicyScope Regular while replacing <New Policy Name> with any name you like.
  3. Also, replace Regular with Organization to apply this policy to all users in the organization.

Reinstall Outlook Connector

If the error message also displays “MAPI was unable to load the information service msncon.dll”, there’s an issue with the Outlook Connector. Reinstall it to debug the error.

Related Questions

Outlook Stuck on Loading Profile. How to Fix it?

This mostly happens because of conflicts between your OS and OEM graphics drivers. However, there may also be other reasons. Check out our article on Outlook Stuck On Loading Profile to find out how to fix the problem.

How to Fix Outlook Not Responding?

We have a dedicated article on 13 Ways to Fix Outlook Not Responding. Check it out to find how you can troubleshoot this issue.