I have created a menu under Reporting menu same as Reporting/Point of sale/Sale Details but when clicking on print button it shows error "RML is not available at specified location or not enough data to print!
(None, None, None)"
My code 
from openerp.osv import fields, osv
import time

class calldata_print_report_wiz(osv.osv_memory):
    _name = "calldata.print.report.wiz"

    _columns = {
        'date_start': fields.date('Date Start', required=True),
        'date_end': fields.date('Date End', required=True),
        'Caller': fields.char('Caller'),
    }
    _defaults = {
        'date_start': lambda *a: time.strftime('%Y-%m-%d'),
        'date_end': lambda *a: time.strftime('%Y-%m-%d'),


     }
    def print_report(self, cr, uid, ids, context=None):
        datas = {'ids': context.get('active_ids', [])}
        res = self.read(cr, uid, ids, ['date_start', 'date_end', 'Caller'], context=context)
        res = res and res[0] or {}
        datas['form'] = res
        print datas
        return {
            'type': 'ir.actions.report.xml',
            'report_name': 'calldata_report',
            'datas': datas,
       }
calldata_print_report_wiz()


i have file calldata_report.rml inside calldetails/report directory. then why it shows the error? Please help