Error Message when opening Outlook (Classic)

Hi @François Godbout, 

I hope you’re doing well today. 

From your description, you are receiving the message “Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. An unexpected error has occurred” when you try to open Outlook (Classic) after you cleaned up files on the device.  

This error commonly occurs when Outlook cannot load the local configuration it depends on, such as the Outlook profile, the mailbox data file, or the Navigation Pane settings. In addition, certain add ins may prevent Outlook from starting correctly even when the mailbox itself is healthy. I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open t… 

Below are some workable options that might be the most appropriate for your current situation: 

1/ Reset Outlook startup settings and check add ins 

• Close Outlook completely. 
• Press Windows key + R, type outlook.exe /resetnavpane, then select OK. 

• If Outlook still does not open, press Windows key + R again, type outlook.exe /safe, then select OK. 
• If Outlook opens in Safe Mode, disable add ins: File > Options > Add ins > Manage COM Add ins > Go. Uncheck all add ins, select OK, close Outlook, then open Outlook normally. 
• Re enable add ins one at a time later to identify which one causes the startup issue. 

2/ Create a new Outlook profile (refreshes the configuration) 

• Close Outlook. 
• Open Control Panel, then search for and open Mail (sometimes shown as Mail Microsoft Outlook). 
• Select Show Profiles > Add, name the new profile, then sign in and complete setup for the email account. 
• Under When starting Microsoft Outlook, choose Always use this profile, then select the new profile. 

• Open Outlook (Classic) and verify the issue is cleared. 

3/ Repair Office and rebuild the local mailbox file if needed 

• Run an Office repair: Settings > Apps > Installed apps > Microsoft 365 or Office > Modify > Quick Repair. Restart the device and test Outlook. 

• If the issue continues, run Online Repair from the same menu (this reinstalls Office components and takes longer). 
• If you use an Exchange or Microsoft 365 work account, rebuild the offline cache file: close Outlook, open File Explorer, paste %localappdata%\Microsoft\Outlook, then rename the .ost file to .ost.old and open Outlook again (Outlook will recreate it). 
• If you use a POP account or a PST data file, run the Inbox Repair Tool: search for SCANPST.EXE on the device, open it, browse to the Outlook .pst file, then run Start and apply any repairs. 

4/ Contact IT administrator:    

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.         

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn    

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.        

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.          

Thank you for your patience and your understanding. I look forward to continuing the conversation. 

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The error indicates classic Outlook for Windows cannot start and cannot open the Outlook window. This is a known startup issue class of problems.

Use the classic Outlook startup troubleshooter to diagnose and fix common startup issues automatically:

1. On the affected Windows PC (Windows 10 or higher), close Outlook.
2. Run the classic Outlook startup troubleshooter from this entry point: select Start on the page and allow it to open the Get Help app.
3. Follow the prompts in Get Help so it can detect and repair Outlook startup problems.

If the troubleshooter cannot resolve the issue, use the same article’s “fix it yourself” section (on that page) for additional manual troubleshooting steps.

References:

• I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”