Having retransmitted segments is perfectly normal. It's more the amount of this error that is an issue.So if the percentage is very high (like 20%) then you may have an issue on your network connection between the Load Generator and your server.
That means one or the other did not acknoledge TCP packets and so the packets was retransmitted.
It may happen on poor connections like with mobile connection or ADSL connection.
You should check with your network team to get more details.