Are you sure all your settings are perfect. If so, then plz follow this steps

./nodetool disablethrift
./nodetool disablegossip
./nodetool drain

stop the service and then delete the all data, saved_caches and commitlog files. Then restart your service.
Repeat these steps for all the nodes. I hope it will work.

Abhijit Chanda
VeHere Interactive Pvt. Ltd.