The solution for this is pretty simple.
In the accept rate plugin there is a file named qa-accept-layer.php, open the file and go to line 38. you will see the following code.
$rate = round($accepted/$total*100);
The error is caused because it is dividing the value by 0. To stop this warning from showing, you must suppress the round function with the error supression operator @.
$rate = @round($accepted/$total*100);
Change the code as shown above, and every thing should be working fine.