ok, I've extracted the zip file, navigated to the directory with the "openvpn" file in terminal and ran the command, now I get a new error message :
options error : in [CMD-LINE]:1: error opening configuration file client.ovpn

how can I replace the openvpn version on the n900 (2.1.1) with the one you provided ? can I copy the binay file from zip somewhere to directly overwrite the older version ?

I've noticed the (2.1.1)