It seems that different tricks worked for different people. But most have managed to get away from that situation one way or another.
groze: Trust me, you're better off not being able to proceed in Broken Sword 4. In fact, it would be better if you hadn't started it altogether.
Obviously, if you're a fan of the series, you want to play all the titles -- I can absolutely understand that, I did the same myself -- but the thing is BS4 is
not a good game at all. While the two first games were groundbreaking and arguably sky-rocketed the Broken Sword series to the pinnacle of point-and-click adventure game excellence, things started going south with the third installment, that fell victim to the 3D-craze of the late 90's/early 2000's. Still, when it comes down to it, Broken Sword 3 does manage to be a somewhat decent and enjoyable entry in the series, despite the shift to 3D and some gameplay flaws, mostly due to it being one of the first point-and-clicks using a 3D engine, and Revolution still experimenting with it. Story, characters and narrative are admitedly inferior to those of Shadow of the Templars and The Smoking Mirror, but at least they're clearly and unmistakably 'Broken Sword-ey', something that Broken Sword 4 never manages to accomplish. Poor puzzle design, a story that tries too hard to be Broken Sword 1 all over again, just to please fans of the series, characters that underwent such bizarre transformations, they no longer feel like the ones we grew to know and love, convoluted, all-over-the-place writing... in short, the worst title in the series, and one I'm pretty sure that if Revolution could erase from history, they would. The only thing it did relatively good was the graphics, as it does look way better than Broken Sword 3, and actually aged quite good, all things considered.
Fortunately, the 3D bandwagon madness of yesteryear has come and gone, and Revolution returned to the great 2D style they excel at (albeit using 3D cel-shaded models for the characters) with Broken Sword 5 -- a superb game, probably up there with the first two, and I can hardly wait for the second part to come out! So, my advice to you would be to either quit Broken Sword 4 altogether, or to use a save file to quickly get you through that part of the game, if you really have the need to finish it, in order to finally move on to the first episode of BS5 and forget 4 ever existed.
While BS4 is the weakest game of the series, advising the OP to abandon the game, when he has nearly finished it, is probably the most unhelpful advice I have ever seen.