Issue in editing the Java Mapping from NWDS

Hi All,

I am working on SAP PI 7.31 SP03.I wanted to write a java mapping and I am following the below blog:

http://scn.sap.com/community/pi-and-soa-middleware/blog/2013/03/13/write-java-mapping-directly-in-esr

I connected to ESR from NWDS. I opened the message mapping with Java Editor, but I am not able to edit the message mapping.I am getting the error saying that there is error in cheching out the object. Please suggest me how can I edit the message mapping. I have attached the error, which I am getting in NWDS.

Thanks,

Madhurima