Why won't the Apex Database install or run correctly after security permissions have been set on the Apex database files?
The MSSQLSERVER service operates under the authority of a service account. The account may be "System", or it may be an account created to run services in a domain. The service account must have full permissions on the directory where the Apex database files reside. It is not important for any specific users to have access to this directory, and in fact it is usually incorrect to grant any accounts other than administrators and the MSSQLSERVER service account access to this directory.