Have you received error 0xc1900204 as part of your SCCM Task Sequence for upgrading to Windows 10? I recently resolved this at a customer where there were three potential causes for the same error! For this blog entry I'll cover what I believe to be the most common cause of this.
Using 1709 (or newer) upgrade media but not specifying a Product ID. Starting with 1709 Microsoft has tried to reduce the number of ISO files created. So they only create two types of ISO files for Windows 10, consumer and commercial. Each ISO contains multiple versions of Windows 10. In our media the education version was index 1 and enterprise was index 3. By not specifying a product key the task sequence defaulted to index 1 (or could not determine) and therefore would not make upgrade available from a Windows 7 Pro/Enterprise to Windows 10 1709 Enterprise. You may acquire a publicly available product key from this MS link https://docs.microsoft.com/en-us/windows-server/get-started/kmsclientkeys. For our enterprise to enterprise upgrade we used NPPR9-FWDCX-D2C8J-H872K-2YT43.
To further identify this as the cause of the error check for one of the following in the setupact.log.
"MOUPG ProductKey: Product key is invalid."
"MOUPG ProductKey: Product key using pkey edition = [Professional]." - Where the edition is incorrect.
"MOUPG MigChoice: Selected install choice is not available."
"MOUPG MigChoice: After Migration Filter -> [CleanInstall | DataOnly | WildCard]"
If you manually run the setup you may see the following with this problem. Keep personal files and apps is greyed out and at the bottom of the dialog is the text "Your files, apps and settings can't be kept because you're installing an edition of Windows that's different than the one you're currently using."
Other causes of this have to do with language differences between the system being upgrading and the media used or potentially problems with windows update corruption.