I converted my Windows Phone 7 project to a Windows Phone 8 project. My project has about seven different configurations. Normally, there would be a Debug configuration and a Release configuration but I added more. The additional configurations let me created apps that have different branding and features all from the same source code.

The Debug and Release versions work fine when I try to test them. I select the ARM processor option and then start the debugger. The app is deployed to the phone and runs as expected. Unfortunately, this is not the case for the other configurations.

"Deployment optimization failed due to an invalid assembly. Rebuild your source projects and try again."

It took me a while to figure out how to get past the problem but I have not actually fixed it. To get past this, I changed the processor selection to Any CPU and then deployment worked.

Microsoft should at least hint at what is making the assembly invalid. So far, I cannot find anything on the internet beside a single topic, copied in many posts and comments, about some library that no longer exists. That is certainly not my problem since I have never heard of that library.

Now I need to figure out why this happens. I don’t need an x86 version of the Windows Phone 8 app. In fact, I don’t understand why I ended up with that selection for my project when it was converted.