After installing Weka/RWeka in R, you may get this error if you try to load RWeka in the same session:
Cannot create Java virtual machine (-4)
Error : .onLoad failed in 'loadNamespace' for 'RWeka'
Solution: Just close R and re-open it.
Cause: Apparently the installation requires some initialization.
Tested on R 2.10.1 on Windows XP.