Splunk DB Connect 2: [ERROR] [rh_connections.py] exception Validating connection with URL .... : Vector Enumeration

[splunk_zen]

Though we could get Splunk DB Connect 2 working flawlessly on our Search Head, repeating the same thing on any of our Heavy Forwarder has not been successful. Even though the Connection shows up as valid (correct Java 8 path, MSSQL sqljdbc4.jar driver correctly deployed, no conflicting sqljdbc.jar in the dir, port 1433 allowed through), testing a query which works on the SH gets stuck at the "Parsing job..." stage, generating:

 [ERROR] [rh_connections.py] exception Validating connection with URL [jdbc:sqlserver://epo.foo.bar:1433;databaseName=ePO_foobar;selectMethod=cursor] failed: java.util.NoSuchElementException:java.util.NoSuchElementException: Vector Enumeration

in the dbx2.log and never reaches "Executing SQL query" as it does on the SH.

What could explain this?

[jcoates_splunk]

works on one but doesn't on the other... there's gotta be a difference between them. That's a java message, so I'd look at JRE and JDBC.