Steps to resolve error---

1-When you are in Composer, with your Documentum Web Service project open, change to the Web perspective. This will allow you to see the referenced DocumentumCoreProject.
2-Navigate down the DocumentumCoreProject as follows: /DocumentumCoreProject/dfs6.5/emc-dfs-sdk-6.5/etc and open the dfc.properties file.
3-Edit this file with the information pertinent to your environment:

dfc.docbroker.host[0]=my_server
dfc.docbroker.port[0]=1489
dfc.globalregistry.repository=documentum
dfc.globalregistry.username=dm_bof_registry
dfc.globalregistry.password=KmYwfPemffMsdfrfprSphRf5Lwazsdfxg\=\=


4-Save the dfc.properties file.
5-Validate and Build your Project
6-Export to an EAR file using the Composer Export Service Archive tool - i.e. right-click your custom Documentum Web Service project and select Export, then choose Documentum/Export Service Archive.