You need to install Rserve_1.8-6, there are some bugs with the earlier version you have installed see the following post for how to do this:
I had to install R-develop and openssl-devel packages on my system to make that work.
However, that should not have caused your problem. Did you try with a freshly downloaded KNIME AP with a new Workspace? Maybe something went wrong with the installation.
best,
Gabriel