How to Fix the New Outlook When It Won’t Start After an Update

Why Is My New Outlook App Suddenly Crashing? A Simple Fix You Can’t Ignore.

You turn on your computer, ready to check your emails. You click on the new Outlook app icon, and for a split second, it seems to open. Then, just as quickly, it disappears. It will not start, no matter how many times you click. If this has happened to you, you are not alone, and it is likely not your fault.

Around August 19, 2025, many people found themselves in this exact situation. A recent automatic update to the new Outlook for Windows application caused it to stop working for a number of users. The problem was frustrating because it happened without any warning. One moment Outlook worked perfectly, and the next, it was completely unusable.

This guide is here to help you understand what went wrong in simple terms. We will look at the cause of the problem, the steps people took to try and fix it, and the final, simple solution that gets your email back online. This information is especially useful for IT support staff who need to solve this problem for others, but it is written for anyone to understand.

The Problem: A Faulty Update Breaks Outlook

The issue began after an automatic update pushed the new Outlook app to version 1.2025.813.500. Apps get updates all the time to add new features or fix old bugs. Usually, this process is seamless. In this case, however, the update contained an error.

Users reported that after their Outlook app updated itself, it would no longer launch. This was not a random glitch affecting one or two people. Reports started coming in from different users, including IT professionals managing many computers in a corporate setting. They all described the same behavior: the app would attempt to open and then immediately crash.

The core of the issue was a technical conflict deep within the application’s code. It was not caused by a virus, a hardware failure, or anything the user did. It was a mistake in the software update package that Microsoft released. Recognizing this is the first step, as it means you do not need to worry about your computer being compromised. The problem lies entirely with the Outlook app itself.

The Technical Clue: What the Computer’s Diary Told Us

When a program crashes on a Windows computer, it usually records a note about what happened. This record is stored in a tool called the Event Log. Think of the Event Log as your computer’s diary, where it writes down every important action and error.

IT professionals checked this log and found a very specific clue. The error message consistently pointed to a single file: ucrtbase.dll.

What is this file?

• ucrtbase.dll is a critical system file. It is part of a software library from Microsoft called the “Visual C++ Runtime.”
• Think of this runtime library as a shared toolbox. Many different applications built by developers use the tools inside this box to perform common tasks, like managing memory or processing text.
• Outlook needs this specific “tool” (ucrtbase.dll) to run properly.

The error log showed that the new version of Outlook (olk.exe) was trying to use ucrtbase.dll in a way that caused a conflict, leading to a crash. The update created an incompatibility. It was like trying to start a car with the wrong key. The key fits in the ignition, but it cannot properly engage the engine, so the car will not start.

Initial Attempts to Fix the Problem

When faced with a broken application, there are several common troubleshooting steps. Many users, including IT experts, tried these logical solutions, but they did not work for this particular issue.

Solution 1: Reinstalling the VC++ Runtimes

The first logical thought was that if the ucrtbase.dll file was the problem, perhaps reinstalling its parent library (the VC++ Runtime) would fix it. Technicians tried this, but it did not solve the crash. This was because the ucrtbase.dll file on the system was not actually broken; the new Outlook update was simply incompatible with it.

Solution 2: Trying to Install an Older Outlook Version

The next idea was to go back to a version of Outlook that worked. This is a common strategy called a “rollback.” However, this also proved unsuccessful. The way the new Outlook app is managed through the Microsoft Store made it difficult to force an older version to install and stay put.

Solution 3: Deleting Cached Data Folders

A suggestion circulated in online forums that offered some hope. The proposed fix was to delete two specific folders from the user’s local application data directory. The folders are named Olk and OneAuth.

• What do these folders do? They store temporary data, cache, and account authentication information for the new Outlook app.
• Why did this work for some? Deleting these folders forces Outlook to rebuild its settings and re-authenticate your account from a clean slate. This can sometimes resolve corruption issues that cause crashes.
• Why did it fail for others? For many, this fix did not work. The reason is that the root cause was not corrupted user data. It was the fundamental code conflict between olk.exe and ucrtbase.dll. Clearing the cache does not change the app’s core programming, so the crash would continue to happen.

While these efforts were logical, they did not address the true source of the problem, which was the faulty code in the update itself.

The Official Solution: A New Update Fixes Everything

Thankfully, Microsoft became aware of the problem quickly. They stopped the rollout of the broken update to prevent more users from being affected. Shortly after, they released a new version of the Outlook for Windows app that corrected the error.

The fixed version is 1.2025.818.302 or newer.

This new update resolves the conflict with the ucrtbase.dll file, and once installed, the Outlook app starts and runs normally again. The best part is that getting this fix is very simple.

How to Get the Correcting Update:

1. Open the Microsoft Store application on your computer. You can find it in your Start Menu.
2. In the Microsoft Store, look for the Library icon. It is usually located in the bottom-left corner of the window. Click on it.
3. At the top of the Library page, you will see a button that says Get updates. Click this button.
4. The Microsoft Store will now check for updates for all of your installed apps, including Outlook for Windows.
5. Allow the store to download and install the new version. Once the update is complete, try opening the new Outlook app again. It should now launch without any issues.

This is the only required step. You do not need to delete any files, reinstall runtimes, or change any system settings. Simply updating the app through the official Microsoft Store provides the permanent fix.

For Advanced Users: Understanding the Event Log Entry

For those who are interested in the technical details, here is a simple breakdown of the German event log entry that identified the problem.

Fehlerhafter Anwendungsname: olk.exe, Version: 1.2025.813.500

Translation: Faulting application name.

Meaning: This tells us the exact program that crashed: olk.exe, which is the new Outlook, at the broken version number.

Fehlerhafter Modulname: ucrtbase.dll

Translation: Faulting module name.

Meaning: This is the most important clue. It names the specific file or “module” where the error occurred: ucrtbase.dll.

Ausnahmecode: 0xc0000409

Translation: Exception code.

Meaning: This is a specific error code that tells developers the type of crash. This code often points to a software bug related to security checks, like a buffer overrun.

Fehlerhafter Anwendungspfad: C:\Program Files\WindowsApps\Microsoft.OutlookForWindows…

Translation: Faulting application path.

Meaning: This shows the exact location on the hard drive where the crashing program (olk.exe) is installed.

This log provided a perfect fingerprint of the problem, allowing engineers to pinpoint and fix the bug in the next update.