Oracle ORA-03113: end-of-file on communication channel

The ORA-03113: end-of-file on communication channel error is a generic error. The ORA-03113 error when connecting suggests that the connection was established, but lost later, like a timeout.
There are many possible causes for the ORA-03113 error.
For example, ORA-3113 could be signaled for any of these scenarios:
- Server machine crashed
- Your server process was killed at O/S level
- Network problems
- Oracle internal errors / aborts on the server
- Client incorrectly handling multiple connections
- Etc

It goes on to note that the ORA-03113 End-Of-File error often has additional messages:
It is common for this error to be accompanied by other errors such as:
- ORA-1041 internal error. hostdef extension doesn't exist
- ORA-3114 not connected to ORACLE
- ORA-1012 not logged on

To find more details, check for a trace file in your USER_DUMP_DEST and BACKGROUND_DMP_DEST directory.