"Unable to activate Windows Store app [GUID]. The [EXE Name] process started, but the activation request failed with error 'The app didn't start'." - Make sure your project is on C!

I spent the day fighting this issue...

Had a Xamarin.Forms app, based on the Cross Platform - Blank App (Shared & also Portable), that worked in the Android emulator, but all the Windows targets would fail. The apps would crash right after start...

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Warning
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A debugger is attached to App4.UWP.exe but not configured to debug this unhandled exception. To debug this exception, detach the current debugger.
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OK  
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Then

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Microsoft Visual Studio
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Unable to activate Windows Store app 'f736c883-f105-4d30-a719-4bf328872f5e_nh7s0b45jarrj!App'. The App4.UWP.exe process started, but the activation request failed with error 'The app didn't start'.

 

See help for advice on troubleshooting the issue.
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OK   Help  
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I did a bunch of repairs, re-installs, etc., thinking it was a Xamarin.Forms issue.

Then I did what all dev's should do when troubleshooting, started eliminating variables. "What happens with a standard, non-Xamarin UWP app?"

Same error! Well now we know it isn't Xamarin!

Finally I came across this thread;

[UWP] Unable to activate Windows Store app, the app didn't start - Windows 10 Universal Apps

What can be the problem here? This only happens on universal apps. Classic Desktop projects opens without problems.

Things I already did, some of which are based on solutions I came across while trying to solve this:

• Install Visual Studio 2015 Update 1
• Check for App.config (supposedly, I should delete this; there no such file so I can't really delete it)
• Build > Clean Solution, Build > Rebuild Solution
• Uninstall the output app on the start menu
• Delete `bin` and `obj` folders
• Change the `Package name` in the Package.appxmanifest file
• Change the output from `x86` to `x64` and vice versa
• Change the `Debugger type` in Properties to `Native Only`
• Tried running as `Release` failed, then reverted it back to `Debug`, still failed
• Tried renewing my developer license. It doesn't work for Windows 10 Universal Apps and is only for Windows 8 Apps.
• Tried uninstalling Visual Studio 2015 completely and re-installing. Still nothing.
• NEW: Tried doing a full fresh reformat of Windows 10 still didn't work.

So yeah, I've pretty much exhausted every solution I can find on the internet to try and fix this. If anyone can offer more solutions, I'd be glad to test it out. ...

All of that is what I did too (Except for the VS/Win uninstall/Re-install)

Scrolling down... no the "answer" can't be it! It can't be THAT simple!

"...I even went as far as to do a fresh install of Windows 10 but when the problem still persists, I was about to give up. But I found out another solution that I haven't tried: move the project folder to the C: drive.

Apparently, when I have the project folder on my D: drive, it wouldn't work and will show me the said error...

OMG, all my projects were on my D drive too! It CAN'T be that, can it?

Move the original Xamarin project from D to C and guess what?

Worked like a charm!

 

There are days when I hate technology...