Unfortunately I have a very similar problem. I have tried drilling everywhere above the window but with the same result, I can push a screwdriver through the plaster and then hit metal or ? which I cannot penetrate and the hole is not deep enough to put a rawl plug in. In some parts of the wall I can drill deep enough for a rawl plug but these will simply not hold anything and three times the poles has collapsed. I have tried an adhesive but that also did not work. I am not too happy with the idea of glueing a batten on to the wall and then the pole onto that and then hanging the curtains. Is there no other alternative at all?