Have you added the nuget package EPiServer.XForms (it has been broken out to its own package)?
Yes, the Episerver.XForms package is added and from what I can see of the fusion logs, the Episerver.XForms assembly is loading correctly. I can see how the XForms assembly tries to override the BackingTypeResolver but this does not seem to happen for me. Not sure if it´s related to how the IOC inititialization is done. The project uses StructureMap initialization direcly but I cannot see what should be causing the error. Will continue trying to resolve it today, but suggestions are welcome :)
I finally found the error. The assembly was marked as non-scannable in the configuration, so the autoinjection to the IOC was never done due to this. Adding an sample of how the configuration looked like if someone else encounters this:
<add assembly="*" />
<remove assembly="EPiServer.XForms" />
I am working on an upgrade of a site to Episerver CMS 11.x and getting a strange error when the BackingTypeResolver is synchronizing models.