network issue after creatingNIC bonding

hi,
i have 2 NIC and create bonding on that ,,previously it was working fine,but today suddenly i am not able to get continues access of same server and when i m pinging same server some times it shows RTO....and some time its pinging......after that i have down one of my NIC...then i am able to get proper access of server

I have physically check there is no any NIC card issue.
Kindlu help