UE4 is not compatible with the latest version of Subversion, which is VisualSVN 4.0, and Subversion client 1.10.4. It took me many hours to figure this out since there is very little documentation online regarding Subversion. When attempting to use Subversion as source control for UE4, I got the error stating that the format version was expected to be between 1 and 7, but the version found was 8. I eventually found out that this was due to the update creating repositories with a new format, being 8, of course.