[LoadUIWeb] Connection 9 of the scenario assigned to the virtual user "Virtual user group (278)" was simulated partially.

The previouse answer is not a solution. It will force the tool to generate less load. And this may hide the errors. But it will not be a testing of the site. It will be a way to say that site is ok while it will not work for that amount of virtual user and the scenario. 

In general every single web server attempting to save itself by closing connections. This means that your test simulates too much traffic for the site ant it doing it's best to survive. The site should be inspected and improved at this point.