DB2 connection rejected with JDBC and ODBC
As I understand it, your development team got the error when using DbVisualizer with JTOpen (jt400.jar) for direct connections to the database.

I got the same exception with DBvis ver 9.1.10. The tool took a long time when clicking the connect button, then finally showed error code -99999. 

What I do to fix this is to disable the Proxy setting of DBvis:


Menu: Tool/Tool Properties
Go to General Tag->Proxy Setting
Check "No Proxy" and restart DBvisualizer.