Petimar,
Also, it could be that the chordsheet you are using was saved with some type of glitch. It's rare but it can happen.
Try the following couple of things...
ONE1. Open the problem SGU/MGU file in Realband and then save it as MGU/SGU with a slightly different name.
2. Now open this newly saved file in BIAB.
3. Check that all tracks are unfrozen and generate.
Does this help?
TWO4. Under "File" select 'New' to load a brand new chord sheet into BIAB.
5. Type in a few chords.
6. Add one of the problem instruments.
7. Generate.
Does this help?
Let us know how you go.
Regards,
Noel