A strange error

Assume I have two array that only have different row count. After sorting data, I refreshed grid with the array that have less row, and then an error occurs.
myData=myDataLessRow;
obj.setRowProperty("count", myData.length);
obj.setStatusProperty("code", "");
obj.refresh();
var howManyRows = obj.getRowCount();
if(howManyRows==0)
{
obj.setStatusProperty("code", "nodata");
obj.refresh();
}

What is the error?