Thank you all. This is all helpful.
A few updates:
1. I dont have a PINMame32.ini. I have a PINMame32ui.ini, but not the former. I think the issue might be a focus issue actually. Sometimes, when a table launches, it doesnt have focus.
2. Also, when I close a table using Visual Pinballs close button, it successfully closes but doesnt return focus back to BigBox.