I had a similar problem when I tried to use SplunkDBConnect (dbx) app, i had similar errors (which were actually a missing mysql driver problem) and the jbridge was hanging all the time.
If you have DB inputs, check that you have the correct driver for DB engine:
http://docs.splunk.com/Documentation/DBX/latest/DeployDBX/Installdrivers
Also, in java.conf for dbx app you might want to add the bridge stanza:
[bridge]
addr = 127.0.0.1
port = XXX
threads = 10
This worked for me!
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