The exception is thrown when EMSCA can not connect to EMS server due to the following:

1).  The EMS server is down.
2).  EMSCA is connecting to EMS with an incorrect user/password. 

If EMSCA is started with the "-j" option, EMSCA by default uses user/password entered on EMSCA GUI to connect to EMS server.
If EMSCA is started without a JAAS file, EMSCA by default uses "admin" with no password to connect to the EMS server.  Check if the password for the "admin" user in the JAAS user configuration file matches that in the EMS server.  Note that password the in the JAAS user configuration file can not be empty.

Refer to the EMS Central Administration Guide: Chapter 2 Running the Central Administration Server : Security Considerations.