ILLEGAL: b b8-b7 on turn 4:
There was no b on b8. The piece on b8 is a r.
Go back with your browser's BACK button, reload the page, and try again.
For diagnostic purposes, here is the full movelist:
1. P d2-d4 
1... p d7-d5 
2. P e2-e3 
2... p g7-g5 
3. P g2-g3 
3... p b7-b6 
4. f1-g2 
4... b b8-b7 
5. P h2-h3 
5... p g5-g4 
6. P h3-h4 
6... P h4-h2;p g4-g5 
7. P h2-h3 
7... p g5-g4 
8. P h3-h4 
8... p a7-a5 
9. B g1-h2 
9... p e7-e5 
10. P c2-c3 
10... p f7-f5 
11. P a2-a3 
11... p e5-e4 
12. P b2-b3 
12... b b7-a6 
13. P a3-a4 
13... b a6-d3 
14. P b3-b4 
14... c d8-c6 
15. B g2-f1 
15... b d3-f1 
16. S e1-f1 
16... p a5-b4 
17. P c3-b4 
17... c c6-b4 
18. S f1-c7 
18... s a8-c7 
19. Q a1-c3 
19... c b4-a6
In case there is a bug in the code, the settings file can be edited at /play/pbm/play.php?game=Cetina+Random+Chess&settings=asymmetric&submit=Edit