The following forum message was posted by tfry at http://sourceforge.net/projects/rkward/forums/forum/165574/topic/3952446: Most likely you are trying to use R 2.12.x with RKWard 0.5.3 (or earlier). For R 2.12.x you will need at least RKWard 0.5.4. Solution: Upgrade RKWard or downgrade R. Regards Thomas