As far as we know now all PCX files on this specific PC are affected. PNGs and TGAs with alpha channel are working fine.

To have the best compatiblity it seems to not use PCX files with auto transparency. But I'm with you that it's not possible to try to fix every single graphic bug that occurs on single PCs.

By the way ... can someone tell me something about PNG support. I read in the manual that PNGs are not suggested, because the display then depends on the DirectX version. Is this still something we should consider? Currently we have some PNGs in use as their creation is much more handy than using TGA.

--- new info (20.04.2012 12:29): after updating the gfx driver to 8.17.12.9610 everything works fine !!!