When the mina IO session fails in certain circumstances you get the error message (the simplest way to reproduce is to use incompatiable mina jars but I think I have seen it can on other cartain socket errors, problem was I needed to be in the degugger to catch it before I added the new error message )

Connection failed: null

which isn't very useful in quickfix.mina.initiator.IOSessionInitiator I changed the code

} catch (Throwable e)

to

catch (IncompatibleClassChangeError e) {
quickfixSession.getLog().onEvent("Libs incompatiable check jar/zip versions. " + e);
} catch (Throwable e) {
// CH e.getMessage returns null unfortunately
quickfixSession.getLog().onEvent("Connection failed: " + e);
e.printStackTrace();
}