Lye in work orders is broken. I usually don't bother any more because 10 bars of soap lasts a long time :-) Just do it every once in a while. I try to automate everything, but soap is a gigantic PITA. It's not just the lye. If you want to have predictable production, you have to use vegetable oil, but jugs don't have stock piles, oil globs don't get counted properly (and you have to know that oil is a glob item), etc, etc, etc.
Having said that, my recollection is that there is a bug in the game where lye that is not in a barrel is not counted in the work orders. This is the biggest hurdle you have to get over. So you make the lye in buckets and then you have to create a stockpile that accepts barrels. However, barrels can hold 100 lye, and you normally don't want to make 100 soap at a time (see below, however), so you make soap when you have more than X lye. However, buckets of lye are heavy and by the time you haul the bucket of lye to the soapery (is that a word?) you're making more lye (because *all* of your lye is now unavailable while you are hauling it). So the trick is to put the lye production right next to the lye stockpile which is right next to the soap making workshop so that you only have to haul it 1 tile.
The frozen thing is actually interesting. It's another bug, but it highlights when you've done the order wrong. All work orders *must* have an item type. If you don't specify one, it basically will either not work or work kind of randomly. For liquids, the way you notice you've done it wrong is that it changes it to "frozen". So the key is to set the item to "liquid", and the material to lye (or as the other poster said the trait to lye-bearing). This is also true for work orders with milk, and other things.
Anyway, the last thing you might do to make life easy for yourself is to make some soap by hand up front. Then just set up a job to make a few lye each month. When you have more than 100 lye, you know that you have 2 barrels with lye in them and you can make soap without screwing things up too badly. Of course, again, there isn't much point because 100 soap is more soap than you will ever use, unless you are building structures out off it...
Yeah, I don't automate soap any more, sadly. I always think it would make a nice trade item since you can't buy soap when you embark (a bit of RP here), but it's such a pain that I don't think it's worth it. Maybe if you have a cave crocodile leather farm and you have lots of rendered fat it might not be *too* bad...