Workflow Email to Customer for Cases

Hi,

I am trying to setup a Workflow rule for Cases where if the customer does not answer the phone, when we set it to Called - No Answer, it would automatically send an email to the customer to ask them to call back. I have tried putting the To address to #Pers_EmailAddress# but when I select the workflow option for Called - No Answer it comes up with "Attempted to send E-mail without any recipients: RuleId = 11230" and does not send an email out.

Any ideas as a bit stuck now

Cheers