Server "XXX" has shut down the connection prematurely
Sounds like you'll want to find out WHY rather than simply ignore the error message to get through your test because with the error, your test is essentially invalid.
I faced this issue once when my load generator machine had reached CPU utilization >80%.
I did some browsing and found that this error can be due to server behavior on larger volume of load.
Design the scenario to perform slow ramp-up load.
Some suggestions: http://support.openview.hp.com/selfsolve/document/KM895362
Can you try the same test with Half the load used , twice the think times and 5 times of Rampup time used. Do you still see the issue ? If you wont then try to comapre the Resource usage and response times.
If resource usage is low and response times wont change and you still see issues on this tests this may be due to slow network.