HTTP/1.1 409 Conflict

Hi,

I have similar code as below to create new work item in RTC.  

URL="https://localhost:9443/jazz/oslc/contexts/_9BHm0EqVEd6HXO10niqZpg/workitems"
curl -D - -k -b $COOKIES -H "Content-Type: application/x-oslc-cm-change-request+json" -H "Accept: text/json" -X POST --data-binary @create-simple.json $URL

However, I keep getting HTTP/1.1 409 Conflict error intermittently.  

HTTP/1.1 409 Conflict
Date: Wed, 21 Dec 2016 12:00:07 GMT
X-Powered-By: Servlet/3.0
Cache-Control: private, max-age=0, must-revalidate
Expires: Wed, 21 Dec 2016 12:00:08 GMT
Vary: Accept
Content-Type: text/json;charset=UTF-8
Content-Language: en-US
Transfer-Encoding: chunked
Connection: Close

Any help is greatly appreciated.

Thanks