Well, it looks like there are no network issues. While push-installing the client, we see the files appear on the c drive of the 2008 server. When BE tries to install, it comes with errors. (first 183, later 1603).
We disabled the Windows Firewall, the virusscanner and the User Access Control. On one server it finally did work (why? we don't know). When we install the client locally we got the next error: Sidebyside event id 59.