I encounter this error when user try to subscribe using email delivery
to one of the report. I have configured the Reporting Services to use
Sharepoint integrated mode. This user is a regular user that has read
access to the report item.
Below is the message detail:
A subscription delivery error has occurred. (rsDeliveryError)
A subscription delivery error has occurred. (rsDeliveryError)
One of the extension parameters is not valid for the following reason:
The account you are using does not have administrator privileges. A
subscription cannot be created for [emailaddress].
(rsInvalidExtensionParameter)
Is it true that user needs to have administrator privilege in order to
subscribe for report? I don't think so, right? 
Regards,
Gunady Ng