From what I could understand on his blog, there's an issue with an audio file that causes an error in the game. He submitted the fixed version to the DLSite but it may not have gone up yet. The link works for me, though.
Edit: Some thoughts on the game. While, for the most part, the basic gameplay is the same (shift + arrow keys for offense, arrow keys alone for defense, special moves if you miss twice), it is quite different from the others.
Firstly, it is 100% first-person, as was the first Boko game. While I like this better, there are some moves that look awkward from this perspective i.e. she has a kissing move that is basically just her with her mouth open in front of you and kissing sounds. Gotta suspend your disbelief a bit more for that one. Secondly, once your health depletes, it isn't game over. You can mash the arrow keys to get back up before the count of 10. I always get up twice at 8 and then fail to meet the count the third time. Not sure if that's scripted, as I imagine just using a TKO would be simpler. According to the manual, holding the down the up arrow key while a knock out is happening initiates a grapple, where button mashing will restore your HP. I haven't tested this yet.
As previously mentioned in the thread, you have a new special move meter. Blocking her blows and connecting with your own builds this meter. Once it's full you can perform a special attack via a yellow circle prompt. If you take too long she'll counter attack. The aforementioned kissing move will drain this special move meter, and while I'm on that topic of that move, I'm not sure what causes it to result in defeat. It's either based on time spent not struggling or simply allowing your meter to deplete.
Another new change is that, whereas in the previous games, hitting shift four times while she does a basic attack would result in a low blow, it will instead initiate her "circle to behind" attack, where she will dodge to your side and back you into a corner, proceeding to send a flurry of punches your way. If you block at least three of her punches in one cycle, you'll have a chance to counter-attack. Performing two successful counter-attacks will end this attack. You may also disable this attack and any other in the SP-Move menu. Note that disabling at least 5 moves or disabling this attack won't allow you to win the match even if you deplete her health. As for actually doing that, well, I've been unsuccessful, and I even managed to beat the first game on the hardest difficult. This one's quite tricky.
And probably the most prominent change is the post-match segments. The match itself is, for the most part, only a fight with little humiliation. Once you're defeated, a scene will trigger randomly or based on the move she used to defeat you (untested). She'll trash talk you and, if you're defiant, she'll do certain things to you until you struggle out of them. This includes a beatdown while straddling, trampling, ballbusting, and even a massage with her breasts. These can go on as long as you allow them to.
I'd say, if you enjoyed the humiliation from the previous games, they're still present in the post-match scenes, but the actual fights themselves are better served to people who wanna get beat up. I never saw her throw a kick, which I know will disappoint a few people. But this entry is at least of the same if not higher quality than the first UFG.
Also, based on his blog, it seems there may be a costume-swap feature in a future update. Neat.