i also got this error and also posted it before, but jcl said that he fixed it, but anyway i found my own workaround. Use .dds map instead of .bmp because it much smaller size than bitmap. f.e. if you have a bitmap around 10 mb big, than you will get a .dds texture with 800 kb.
i hope you understand waht i mean. so you just have to convert all bmp´s to dds.