In windows OpenERP 7.0

Filter Based on previous month the below code added [it shows issue]:-

<filter string="Prev Month" name="prev_month" domain="[('data','&gt;=',(context_today()-relativedelta(months=1)).strftime('%%Y-%%m-01')),('data','&lt;',time.strftime('%%Y-%%m-01'))]"/>

In Chrome Browser shows issues:- Uncaught TypeError: Cannot read property 'length' of undefined

In Mozilla Browser show issues:- TypeError: results.group_by is undefined http://localhost:8069/web/webclient/js:3208

Filter Based on Current Date - 90 Days the below code added [its working ]:-

<filter icon="terp-check" string="Data [Today - 90 days]"  domain="[('data', '&gt;=', (context_today() - datetime.timedelta(90)).strftime('%%Y-%%m-%%d') )]"/>

How to solve this issue in filter based on previous month?

Thanks in advance