Long time no speech. My case was similar. Event was success but nothing in Message Log.
Try the following (make sure you are logging SBO events in B1i):
1. Raise your event in current SBO Company
2. Go to Integration Solution for SAP Business One (the Web Interface) and choose 'Monitoring'->'B1 Event Monitor' and view the success list
3. Find your SBO event and keep the Target B1i Application in Mind 
4. Choose Message Log and hit the button Last Exception
5. You may found your entry beginning with the Target B1i Application content. Here you should see what error cancelled your process!
Hope it helps