brundlefly
I'm fairly confident that transposition is the correct answer. A lot of bass synths/patches are programmed to sound an octave or more lower than written. I presume the intent is to make them easier to work with on a 61- or 49-key controller. The easiest way to deal with pre-existing MIDI files that don't use this convention is to enter a positive Key Offset value in the MIDI track.

When Mauryw starts the IS Bass, using the midi data, he said that the IS Bass becomes unresponsive. I don't believe that out of range notes will create an unresponsive soft synth. This is a symptom of the intercept NRPNS function. Peace!    

Kirk Armstrong
I was also having trouble with SI-Bass and Dimension Pro as well. Dave000's suggestion about checking the "Do not intercept NRPN" worked for me as well as transposing the octave.
 
Thank you Dave000. I had been having this problem for a couple of days.

Thank you :) But a tech at Cakewalk told me about it years ago... So :)

I had a number of similar issues with SI-Bass (although in the case of a Karaoke track, there could be SysEx messing you up as well). I also found that my MIDI buffer caused me problems with this instrument until I set the buffer higher.
 
This is not what you asked, but I bought three Scarbee basses from Native Instruments (Rick, Precision, and J-Bass), and the J-Bass alone covers 90% of my needs (with the disclaimer that SI-Bass sounds more like a Precision bass to me but not as live).  I am a big J-Bass guy and use the Rick for special things.
 
The Gibson 5-String Craig created that is available in the Cakewalk store is also excellent and will probably do most anything you need.  If I had bought it first, I may or may not have bought the Scarbees, but since I am most familiar with them, they tend to be my defaults.

Excellent tip! I'll have to remember that one as I've often had issues using downloaded midi files. I'm reluctant to allow the send system exclusive info. In the days of my outboard gear that sometimes messed my sound modules brain up and I'd have to do a factory re set. 

Cactus Music
I've had issues using the SI bass in the past. It seems a little buggy for some reason. On my old computer it would often cause the audio engine to stop. So stopped using for a long time. I tried it the other day with my new computer and it seems fine now. And yes for some reason they have set it in a non standard note values. I have to transpose up 12 ( 1 octave) from what played fine in TTS-1. PS try the Jazz bass patch the default sucks. 

Part of this is that the default preference in sonar for base octave for pitches is (C)0 when the default for the sfz format and synths that run on that spec is (C)-1.  Throw in the fact that NI instruments use c-2 then it gets a bit confounding!