Resolution:
TIBCO Administration maintains multiple database connection pools upon starting. The max database connection number for each pool might be read from different locations. Find the difference of max DB connections in the following files.

1). AdministrationDomain.properties
Connection pool created mainly for managing SYS data.

2). AuthorizationDomain.properties
Connection pool created mainly for managing AUTH data.

3). tibcoadmin_domainname.tra

Connection Pool to POF (Persistent object Framework) Database. This number is always set to 10, by default. Increasing max database connection through Domain Utility will not affect this number. If there still is not enough database connections when the max number is reached, the number specified by tibcoadmin.database.maxConnections in file AdministrationDomain.properties will be used. Users should always use Domain Utility when modifying domain database configuration. Manual modification to the files mentioned above is not recommended.