When running Setup.bat from a source build of 4.21, the following file isn’t currently able to be downloaded: http://cdn.unrealengine.com/dependencies/UnrealEngine-4395058-c8623837b50d45139b973e47f490f4a6/1af8affb9108ea48b07da887db2be691f09da6b6
It currently returns:
<Error>
<Code>AccessDenied</Code>
<Message>Access Denied</Message>
<RequestId>XVK7ZCRBYVAN09HZ</RequestId>
<HostId>VQahiZz4H22lOZi9zVwSIn6BiB7QhufrrEGTm1ksBVm5K3hlj4srWOm2xrTul0bXLFAHHn6YPRE=</HostId>
</Error>
This also prevents any subsequent files being downloaded too, and therefore source builds of the 4.21 editor.