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Fix ClickOnce application not launching

The Office 365 Hybrid Configuration Wizard uses the ClickOnce as deployment technology. While this is great, there are a lot of problems. For example, the ClickOnce application is not launching, or the ClickOnce application cannot be started error. While this should be an easy process, it takes a lot of frustration for most of us. You want the ClickOnce application to start, nothing more. In this article, you will learn how to fix ClickOnce application not launching.


ClickOnce is a deployment technology that enables you to create self-updating Windows-based applications that can be installed and run with minimal user interaction.

The web browser Internet Explorer works out of the box with ClickOnce. You only have to set the .application to open with Internet Explorer so it can start as shown here: Office 365 Hybrid Configuration Wizard can’t start.

But sometimes, it doesn’t work with Internet Explorer, and you can’t start the application. Also, Internet Explorer went out of support on June 15, 2022. So you might not have Internet Explorer running on the machine.

ClickOnce application cannot be started

If you have run the Hybrid Configuration Wizard, you can uninstall it from Programs and Features in Control Panel. Nothing will happen to the configuration because it already applied the settings in Exchange on-premises and Exchange Online.

Open the web browser of your choice and go to

It will download the RunOnce .application file.

Fix ClickOnce application download completed

Open the downloaded .application file, and it will show: Application cannot be started. Contact the application vendor.

Fix ClickOnce application cannot be started

Sometimes nothing happens.

Fix ClickOnce application nothing happens

So how do we get the RunOnce application to work? Let’s look at that in the next step.

How to start ClickOnce application

Step 1. Install the ClickOnce browser extension.

Find the extension on the add-on webpage for that browser:

In this example, we will search for Breez ClickOnce extension and click on Add to Firefox.

Fix ClickOnce application Breez

Step 2. Click Add to install the extension.

Fix ClickOnce application Breez add

Step 3. Click on the downloads icon and click on breezclickoncehelper.exe.

Fix ClickOnce application Breez Helper

Step 4. Click on More info.

Microsoft Defender SmartScreen more info

Step 5. Click Run anyway.

Microsoft Defender SmartScreen run anyway

Step 6. The Breez ClickOnce Helper was installed successfully. Click OK.

Fix ClickOnce application Breez Helper installed

Step 7. Go to Programs and Features and verify that Breez ClickOnce Helper appears in the installed list.

Fix ClickOnce application Breez ClickOnce Helper

Step 8. Close all the web browsers.

Step 9. Start the Firefox browser and insert the URL

Insert URL

Step 10. The Application Install window shows up, and you can click on Install.

Application install security warning

That’s it!

Every time you need to open the RunOnce application, copy-paste the URL into your favorite browser, and it will start the application immediately because it’s already installed.

Read more: Export Office 365 mailbox to PST »


You learned how to launch ClickOnce applications easily in every browser of your choice. First, install the ClickOnce extension and the installer. After that, ensure that you close the browser. Finally, start the browser and visit the URL to run the RunOnce application.

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ALI TAJRAN is a passionate IT Architect, IT Consultant, and Microsoft Certified Trainer. He started Information Technology at a very young age, and his goal is to teach and inspire others. Read more »

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