Microsoft Outlook cannot be opened because of a problem. Contact the developer to make sure Microsoft Outlook works with this version of Mac OS/OS X…

The week before, in my day job as an IT technician, I received a request to help a professor with her Microsoft Outlook app. She hadn’t been at her Mac in a several months (pandemic and all), and now when opening Outlook it would barely even bounce before crashing and popping up an error message that read,

“Microsoft Outlook cannot be opened because of a problem. Check with the developer to make sure Microsoft Outlook works with this version of OS X. You may need to reinstall the application. Be sure to install any available updates for the application and OS X.”

The troubleshooting steps were interesting for this one, so follow me through the process.

1: Check the other Office apps

The professor’s only issue was with Outlook, but she hadn’t tried the other Microsoft apps. Naturally I started with Word and didn’t find any issues opening it, typing in it, or saving documents. Same with Excel. So the issue was not with Office as a whole. So my next thought was to…

2: Update the Office Suite

Microsoft has an auto-update tool packaged with the Office Suite that check for and will install updates to the Office apps either manually or automatically. You can get to it by opening any of the Office app, such as Word, and then hitting “Help” in the menu bar, and “Check for Updates”.

If that doesn’t work, such as if you can’t open any Office apps, then you can find it by opening the Library, then the “Application Support” folder within that, then the “Microsoft” folder, and finally the “MAU2.0” where the app resides. If you’re not sure how to get to this, open a new Finder window, hit the “Go” menu in the menu bar, and hit “Go to folder” and type in the following:

/Library/Application Support/Microsoft/MAU2.0

In this case the apps were out of date, but not by much, so I updated them. These updates still resorted in the same issue. So the next thing was to look for were…

3: Multiple Versions of Office installed:

2 Finder windows, with the top showing Office 2008 and the bottom showing Office 2011.  Image courtesy of Microsoft
Microsoft’s example image of 2 versions of Office installed simultaneously. Image courtesy of Microsoft

So this is a bit particular to this particular problem, especially since Office tends to do better with older versions running alongside the newer versions. That said, Microsoft lists that as a potential fix in their documentation in their article about this very issue. But in this case that wasn’t an issue since the machine only had the current version of Office. This led to the 4th step.

4: Reinstall Office:

Since working with the existing version of Office didn’t work, I needed to uninstall and reinstall Office. I decided to use my favorite uninstall utility on the Mac, “App Cleaner”. While there are a few things that get left behind when using it to uninstall Office, I’ve never had an issue using it to uninstall any app and get the core and some auxiliary parts of the app, including those that typically are causing the issue (except for the Adobe Creative Suite, but you can read how to do that here).

After App Cleaner did it’s thing, I deleted the Office files from the Trash, and then rebooted. Since the user had a subscription of Office 365, we were able to reinstall it from the Office website at after having her login. In this case, however, Outlook still had the exact same issue as before. This finally led to what solved the problem.

5: Updating Mac OS (it works!):

While working on her Mac, I saw it had a notification that it had some updates pending. Given the security updates that came out a couple of months ago, I didn’t think much of it and figured I would run them after fixing Outlook. However, while waiting on the reinstall, I pulled up Software Update and found that the machine’s pending updates were for Mojave version 14.6. Looking at her machine, I found the machine was still running 14.0! I was surprised this was not caught by our management tools (but I fixed it afterwards), given how many updates this machine had not received. For good security measures, and since the issue with Outlook was still happening, I let it update to 14.6.

After the update finished, I checked Outlook and lo and behold Outlook was opening and operating fine. I let it update once more to bring the latest security patches in line, and confirmed it was working The professor was later able to confirm she could login and had no further issues.

What I suspect happened is that Office updated at some point either on its own or through the management tools, and Microsoft hadn’t tested it working further back than a certain revision of Mojave and was perhaps relying on something that wasn’t present. So once it finally had that, it was able to load.

So if you’re having this error message in Office, I’d certainly run through these steps, but it might not hurt you to check if your Mac is running the latest revision of your OS version. If nothing else, this is just another reason to keep your Mac (and any computer for that matter) up to date with its security patches.

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