Charlie, the same thing happened with the .XML file of my second song with more than 255 bars in it. Also, what I said previously about RB generating each track in two consecutive stages is not correct. RB generates the first 240 bars of each track (except for the drums) first and then starts the process all over again with the remaining bars for the first track and does the same with the remaining tracks before it finishes by generating the entire drum track.

Before I try your test, I'd like you to regenerate all of your tracks if you still have your test file in RB or on disk. But this time, I'd like you to watch the text info in the white bar at the top of the RB window. That text info will start by saying "Generating RealTracks Instructions." Then it will start to generate the first 240 bars of each track for each instrument that is included in the BiaB style except for the drums. This means that if you have four instruments (bass, piano. electric guitar, and acoustic guitar), RB will generate the first 240 bars four times (once for each instrument) before it starts over by saying "Generating RealTracks Instructions" again prior to generating the remaining bars for each instrument. When it is done generating the entire track for each instrument, then the Tracks window will shift all the tracks to the left so that bars 240 and 241 are visible with a dark line (the play tarting point) on the boundary between these two bars. This happens at the same time that the dialog box for generating the drum track appears.
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Tom Levan (pronounced La-VAN)
BiaB 2021 Win UltraPAK Build 833, Xtra Style PAKs 1-11, RB 2021, Windows 10 Pro 64-bit, Intel Q9650 3 GHz, 8 GB RAM, 500 GB SSD & 2 TB HDD, Tracktion 6 & 7 (freebies), Cakewalk, Audacity, MuseScore 2.1 & 3.4, Synthesizer V