The Documents service is not enabled for this Portal or a parent Portal

Go to the Webcenter Portal login

1. http://hostname:8888/webcenter. Login using Administrator credentials
2. Click Administration link.
3. Click Portal tab
4. Click on the Administer link for the portal
5. Click on Tools and services
6. Select Documents
7. It may give an warning You have enabled a tool for the portal and you have been granted permissions on this tool.
Configure the security for the tool on the Security page in the portal administration, setting portal member access using Advanced Permissions on the Roles tab.

It will solve the issue.