Update Opportunity close date for new records through workflow

Hi All

 As per the business need we need to update Opportunity close date to system date when the sales stage is changed to close/won. To achieve this we have created a workflow on Opportunity which triggers when a new record is saved. On this workflow we are trying to update the Opportunity close date to system date. We are getting access denied for this though opportunity is getting created at the back end. Is it possible to update Opportunity close date for new records through workflow?

thanks

thanks