I have created port channel between CSW1 & CSW2 using port 23 & 24. If I disconnected the Cable from CSW1 to MX1, my test machine is still able to ping to other location machine through (site to site VPN). But If I disconnect the cable from port 23 or 24, then unable to ping the other location machine from test machine. I checked, when ports (23 & 24) are in aggregate then both ports are up & working fine. As I disconnected the cable from port 23 CSW1 then port 24 gets in blocking mode on CSW2 & same port is on forwarding mode on CSW1 (Root). Please suggest, why port 24 gets in blocking mode on CSW2 due to this traffic is not passing through from one location to other location.
ps. Your are probably experiecing port block issues due to the switch spanning tree priority. If you forcibly make CSW1 the root (for example by giving it a priority of 0) and CSW2 the backup root (for example by giving it a priority of 4096) then it will probably be happier. You should do this anyway on your core switches for stablity reasons.