I had an RGL as well; I had chosen my character and started the game, but once on the world map I tried to access my inventory, just out of curiosity, and I immediately got an RGL. I'm afraid I couldn't read the RGL, because I am unable to get them visible on screen for some reason. I didn't used to have this RGL problem but for many months now whenever I get an M&B RGL I can't get the error message on screen. It might well be the same as the message Froggyluv detailed in his post however, since it occurs when I accessed the inventory. Hope this helps.
EDIT: Started again, and I went to the 'battle' map via the camp menu. I was equipped with a sword and a spear, but the sword was invisible. The scabbard with the sword is visible, and when I draw the sword the scabbard remains but the sword is no longer in the scabbard (as it should be , obviously). The sword is in the hand, just not visible. You may well know about this Nijis, as you said many parts of the game aren't usable yet.
I started briefly playing the game as one of the Lords as you suggest in the download notes, and it looks very interesting and detailed. I wasn't sure how to sleep at a city or in the wilderness (from the camp menu), perhaps this isn't enabled at the moment? Anyway, I could control my fatigue by stopping periodically on the map and resting, but could not sleep. I presume the 100% sleep deprivation was slowing me down, but I hadn't taken note of my original speed so couldn't be sure. As you said, many parts of the game aren't usable at the moment, but just for the benefit of others who are trying this out, I should mention that trying to use any of the market options (armourer, main market etc) results in an RGL for me, as does trying to access the inventory.
Anyway, thanks for uploading this for us to examine, I'll take a more thorough go tomorrow