Polling triggering build even without changes

I am getting this when i tried to set up the builds to run whenever a change occured in the cvs. In the configuration of the job i have mentioned the CVS root and specified the modules of the cvs where the code resides. Apparently this is something to do with the workspace.
Even though the poll scm schedule was set to scan cvs every 20 mins for any changes to the source code, it triggers a build every 20 mins even when there are no changes.
In the advanced options legacy and update options are checked.
Can anyone please suggest what can be done?

Started on 31-May-2011 3:08:34 AM
Workspace is inconsistent with configuration. Scheduling a new build: No CVS dir in /data/users/smpbuild/hudson/workspace/SIS_TRUNK_BUILD/sis
Done. Took 0.26 sec
Changes found