[Therion] Fatal Error in Wish - Tk_GetPixmap

Hi, I'm getting sometimes an error in Wish: "Fail to create pixmap with Tk_GetPixmap in ImgPhotoInstanceSetSize". It seems that the background image in the map editor is too big. However sometimes it occurs only by changing the zoom level, ie from 200% to 100%. What is the maximum image size therion can use as background image in map editor? Best regards Wolfgang