Endless trouble with HDMI output (Bitec IP core)

Well, yes, we purchased the IP core and I'm in contact with Bitec in order to resolve the issue. But somehow it is not progressing. I asked on the forum, just in case someone else has had the exact same problem and might have a quick fix. Although admittedly the probability of that plus that this particular person also sees my post is relatively low :-) Thank you for your answers, though!