I talked to agricultural engineers where I live. They said the grapes were exposed to a lot of medication and were done just after sunset in the evening. (I started spraying as the sun started to set) Could that be the reason? I have never sprayed at night or in the morning.  

If the problem is caused by pesticides, most grapes will have scabs at the bottom of the berries. The grapes in this photo have irregular scars. There may be other causes. Has this happened to the whole vine?