What could cause this error?

Upgrading vCenter Server with Microsoft SQL database fails with the following error message:
The DB User entered does not have the required permissions needed to install and
configure vCenter Server with the selected DB. Please correct the following error
(s): %s
What could cause this error?

A.
incorrect ports open on SQL Server

B.
incorrect database on the SQL server

C.
incorrect compatibility mode on the SQL server

D.
incorrect permission on SQL Server database

Explanation:
https://pubs.vmware.com/vsphere-50/index.jsp?topic=%2Fcom.vmware.vsphere.install.doc_50%
2FGUID-5AA32F87-270C-4171-8896-41A607F8F997.html