The Unattended Service Account cannot be set for the service application. The Secure Store Service key might not have been generated or properly refreshed after the service was provisioned.

This is the error when you get it while configuring the Performance point service application in SharePoint 2010. Once we are done creating Performance Point application, we need to do the configuration part where we need to define the unattanted service account for the application. It is linked to secure store service. Follow the below steps to resolve this issue:-

1) Go to central admin- Manage service applications and check for secure store service. if its not there, create a new one.
2) Once its created, select the services and click on the top ribbon for generating new Key. Once its done, go back to Manage service application page.
3) Under Performance service, click configuration and add the unattended account again and click ok. It should not throw error as the encrypted key was not created. You are ggod to go now and go ahead and create a new site using Business intelligence template.