Problem:

The following error occurred after re-installing XDB:

IMS LOGON ERROR FOR XDB.  RETURN CODE=   -2161               
XDB Error: -2161                                             
XDB not properly installed                                  
SEVERE LOGON ERROR - EXIT DISABLED                  

Solution:

The IMS LOGON ERROR indicates that this is an IMS program. The current SQL Switch is likely set for a DB2 program which causes the issue.