Now I am running into this new error. I think all problem is because of version mismatch. The yum repository is provinding older version of everything.
memcached is installed, libmemcached is installed but now when I run, I don't see memcached in phpinfo(), I have double checked but it is not there. Also path is right. The memcached.so is also there but its not showing in phpinfo().
After so long struggle I noticed error in my apache error_log
memcached.so: undefined symbol: memcached_result_flags in Unknown on line 0
So I think problem is somewhere , may be module is not right ?