Ok I'm going nuts with the 18th mission (kill the pig one). My archers most of the time say can't target and even when they can target they shoot super short range that hits the ground in front of them.
This mission is kinda ruining the whole game since I can't get close to the castle without getting slaughtered en masse. And this is on the easy setting.
So anyone know how to skip this mission or at least how to fix archers so that they can pick off the crossbowman on the towers (funny thing is I could pick of all crossbowman on 3 towers (1 left and 2 right of the gate) but couldn't do shit to the ones on the gate (gate is lower so it should be easier to hit).

This mission is possibly the hardest in teh whole game - it really gets a lot of people stuck! (he says as he is also stuck on this one)
As for archers in Stronghold archers will not move into range when you give them an attack order - they remain where they are and will only shoot from there. Thus you have to manualy move them closer until they are within range and then give them the attack order. This is good as it means that attack orders given to won't suddenly break your defence line or have your archers march out of your castle to get into range during a siege.
Also they seem to do better when you give them a specific tartget to shoot rather than just letting them shoot at anything within their range.

Strangely enough the enemy didn't react to my tunneliers so they could walk in to their camp and tear down most of the towers... Bug but still very decent.
Problem with archers is that they fire but their shots fall like 10m in front of them instead of going towards the towers. Also line of sight is very strange in the game.
Anyway since than I've moved to custom made maps and making insanely strong fortresses. Building it is the fun part for me in the game (too bad about the sprite limitation being so low).

That mission is extremely annoying and require very high amount of micro management (well can do, I'm sure there are better people then me who didn't have problems).
What I did was basically use 2 archers for most of the time - was slow, tedious and annoying but I got through it.
I started in the lower left corner (where all your troops start), and then I moved 1 archer as close to the lower left tower I could without getting fired upon and started tweaking the position until he could in fact strike one of the enemy archers. Then I moved a second archer near and tried with him as well, if successful - the two archers would stand there plinking away.
Then I took 2 more and moved to the lower right corner and did the same.
Extremely tedious and annoying - but eventually I managed to pick off a few of the archers.
After which I moved on to the next one, and next one.
Eventually I had the towers cleared and I moved a larger group close to the central crossbowmen and used "attack ground" and used the downfall of arrows to clear those groups I couldn't otherwise target.
Doing this tactic of moving 2 archers around and picking off single targets I managed to clear out the entire front of the castle.
After that I filled the moat in front of the gatehouse and moved all my archers right up to the gatehouse.
Apparently the computer enemies couldn't hit my archers there, but using ground attack, I then cleaned out the groups of crossbowmen and archers on the inner gatehouse and towers.
Now it was time to attack and I just took a large group of macemen and smashed down the gatehouses and set half of them free (aggressive) and the other half ran straight to the pig and wacked him.
Stupid mission - as said tedious and long - which really caused me to loose interest in the remainder game, so I still aren't done yet, but lack 2 or 3 missions.