This is probably the cause of the problem: From the manual look under texture

"3D cards can not render arbitrary texture sizes. They require power-of-2 texture sizes (32, 64, 128, 256, 512, 1024...), like 64x128 or 128x512. All other sizes are automatically 'inflated' by the engine to the next power of 2, however at cost of video memory, performance, and image quality."

cheers