"HTTP/1.1 500 Internal Server Error" when ran with more than 1 thread - SoapUI Pro 4.5.1

Hi Team,

I am trying to run a load test using SoapUI Pro 4.5.1 . When i ran the test with 1 thread,everything is working fine irrespective of the Strategy selected.

But when i ran with more than 1 thread i see the following Error in the log. Can someone help me fix the problem?

Tue Jul 07 13:24:01 EDT 2015: DEBUG: Attempt 1 to execute request
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Sending request: POST /TempWeb/TempConversionSServiceV1 HTTP/1.1
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Receiving response: HTTP/1.1 500 Internal Server Error
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Connection shut down
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Attempt 1 to execute request
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Sending request: POST /TempWeb/TempConversionSServiceV1 HTTP/1.1
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Receiving response: HTTP/1.1 500 Internal Server Error
Tue Jul 07 13:24:01 EDT 2015: DEBUG: Connection shut down

Note : I am providing a fixed cookie in the Soap request.

Thanks,

Subex