I have a raster file and I want to perform the method "polygonize". Then the problem occurs, that is shown on the screenshot. It doesn t have anything to do with the rasterfile format, I veryfied. Other functions in the same menue(Raster->Conversion do not work either, because of the same problem). I m using the newest version of Qgis (1.8). Older threads here couldn t (as far as I saw) help either. So: I want to ask if anybody has an idea how to solve this problem? Thanks.