It just started doing this.  I'll press down to save, and the game will lock up for a couple seconds until it's done saving.  I downloaded a new copy and ran it from its own folder without any new levels, and it does the same thing.  What's going on?  How can I fix this?

I'm running 64-bit Windows 7, should that be relevant.  Again, I have not had this problem before now.

Figured that I'd start a thread about it; it might help us to see less of it in the future.

Anyway, I'll start with a list of design decisions that I can't stand, and anyone else can post their own pet peeves below.

Slippery walls that only exist because the author couldn't be bothered to think of another way to constrain the player.

Slippery walls have their place, and, if employed properly, can really enhance a level.  (See the Water Temple in Infestation for a good example of that kind of thing.)  Most of the time, though, they're just cheap ways to keep the player from progressing until they've found a jump powerup, or to prevent them from accidentally exiting the level.  That's nothing but a cop-out, and it feels really cheap.  You might be able to get away with it by distinguishing climbable and slippery walls with different graphics, but it takes skill to pull that off, and it often feels just as forced.  (For example, Yggdrasil uses altered tiles to show where slippery walls are, but the walls themselves are so arbitrary that it makes no difference.)

Disguising a chomper an eater with grass or similar scenery.

I don't know if there's even an official name for those things that lie in wait underground to devour unsuspecting players, but I've always called them chompers. Disregard that; there is an official name.  And there are few things worse than using them in places where they can barely even be seen.  Every time that it happens to me, I picture the author going, "Ha, ha!  I got you!" and then running off to, I don't know, pick his nose or something.

Hidden spikes as a cheap way to increase "difficulty".

I see these things used most frequently in three contexts: they're in places that the author doesn't want me to climb, they're in places that otherwise make me let my guard down, and they're in "mazes" of spike-covered blocks that I have to jump through.  The first two uses tie in somewhat to the previous items on this list; my comments there apply here, too.  That third use can work very well, provided that the author makes it possible to divine where to jump without resorting to trial and error, but, sadly, it's often just a way to artificially lengthen playing time by keeping the player "occupied" with dying repeatedly, and that's never good.

Making the player go without the run powerup for more than three screens.

You'd better have a really good reason for pulling this one.  Again, it isn't like I haven't seen levels that do it well, but most examples of this that I've seen seem to have been designed solely to test my patience.  Not good.

Over-reliance on pixel-perfect jumping tests.

I like a good, challenging jump every once in a while.  It's far more satisfying to just barely make it across a gap than it is to hop over it with three tiles to spare, and few things feel more impressive than scaling an irregular surface without being able to double-jump.  But, please, don't overdo it.  That elation quickly turns to frustration and exhaustion when the player finds out that they have to make the same jump three more times in order to get to the next save point.  (Timecraft, I'm looking at you.)

Trying to out-The Machine The Machine.

This is, by far, one of the lamest approaches to level design that I've seen - and, sadly, it's also one of the most common.  You have the same environments, only less atmospheric, the same backtracking, only less fulfilling, the same contrived premise, only less distinctive.  Heck, a lot of these levels even end their opening narration with "This is what happened next:" or a similar phrase.  What happens next, though, usually comes across as more of a Chinese knockoff cheap imitation of Nifflas's style than as something worthy of consideration in its own right.  If you're merely going to rehash a four-year-old approach to level design that was executed perfectly well the first time around, why are you even bothering with your own level in the first place?

Also of note are flaws in execution that, while not exactly pertaining to design, are sloppy enough to make a level far less than what it could be:

Solid scenery.

Self-explanatory.  While mostly confined (thank God) to those near-clueless first-time efforts that inexplicably make it to the archive (Why do people upload those things, anyway?  Do they really think that someone is going to download a level with a name like "destory the robots"?  Or that anyone who would is going to make it past the first screen without immediately thinking about uninstalling it?), I did see it in the otherwise excellent Caverns (and intentionally, at that - never before had I seen a tree silhouette used as a platform, and I dearly hope that I don't see one again) so I thought that it warranted inclusion here.

"Blocking" the player's path with obstacles that the player can overcome.

The only jumping test more irritating than the fourth one in a row is one that leads to a void.  Sometimes, a level author, thinking that their inability to traverse an obstacle marks it as an absolute boundary, will use it at the edge of a level in order to keep the player from merrily running off into a purple oblivion.  What they don't count on, though, is the player, convinced that it hides some necessary item or area, trying over and over again to get past it, realizing only after this arduous challenge that it was all a waste of time.  I actually discovered wallswims by somehow making it to the edge of an "impassable" lava flow and climbing the wall, only to find myself stuck inside a wall in a completely different part of the level.  Needless to say, I was less than thrilled about this.

Lack of atmosphere or variation in structure.

OK, so this doesn't really affect gameplay in any way, but it's a very noticeable detriment.  Long, flat stretches of ground (or floor, as the case may be), unadorned by such needless indulgences as "elevation changes" and "scenery", may be easy to create, but they commit a cardinal sin of level design in being really, really boring.  (To Travel So Far is a near-perfect example of what I'm talking about here.)  You don't have to go overboard and make everything an overwrought mass of ledges and flowers, but atmosphere is a big part of Knytt Stories, and it's a bad idea to neglect it.

All right; I'm done.  Reply as you see fit.