problem with AbstractSnapshotTask

Hi,
I trying to extended the data warehouse for storage any custom field.

I have set "Plug-in Development"->Target Platform with this path \server\update-site.

I have this error "The type com.ibm.team.repository.service.async.AbstractAutoScheduledTask cannot be resolved.
It is indirectly referenced from required .class files" when I try to write this class:

package com.ibm.team.datawarehouse.service.odc.internal;



import com.ibm.team.datawarehouse.service.AbstractSnapshotTask;

import com.ibm.team.datawarehouse.service.ISnapshotService;

import com.ibm.team.datawarehouse.service.odc.IOdcSnapshotService;



/*

 * This class is used by the plugin for automatic snapshots.

 */

public class OdcSnapshotTask extends AbstractSnapshotTask { 



    private final static String TASK_ID = "OdcSnapshotTask"; 



    @Override

    public String getTaskId() {

        return TASK_ID;

    }



    @Override

    protected ISnapshotService getSnapshotService() {

        return getService(IOdcSnapshotService.class);

    }

    	

}

Any suggestions?
Regards
Andrea