Stuck as in the game crashes, or stuck as in it's just too difficult?
Stalkers is a SUPER-hard level, I'd highly recommend going back and playing Alien Side Mission 1 (Maternal Instinct) over and over to level up your Alien. Beating that level will generally net you 30,000+ XP per play through, and that's just points from killing enemies. You can't actually "fail" it unless you die, you just get bonus points for each egg saved. It's by far the most profitable side mission in terms of XP, and it takes like 5 minutes to play.
A few other helpful tips for that level:
- learn to love the Acid Pool ability - it makes Shield Synthetics drop their shields instantly, and if you can get a flamethrower Marine to walk over it you'll weaken him considerably
- Dash Through is also really handy, as you'll deal damage against enemies without getting stopped by them - if nothing else you can cheese your way through fights by just dashing through enemies over and over until they die or you can execute them
- when you get to the sentry gun up on the cliff that fires on enemy Aliens, try to time your passing in front of the sentry gun for when it's mowed down most of the enemy Aliens. The Aliens respawn infinitely, so if you wait too long you'll get mobbed by a fresh set of 4 when you cross in front of the gun. If you time it right, you can end up only having to fight 1 or 2 surviving Aliens.
- when fighting Aliens, take it slow, abuse Dash Through, and let your health recharge - other than the sentry gun bit, there's limited numbers of them. When you see one spawn, back off a bit and let it and its friends come to you, deal with them, and then move forward. Probably the hardest "fight" is when two Warriors attack you simultaneously while you're in range of the Predator's shoulder cannon, but the Predator is on a rock ledge you can partially hide underneath to avoid his gun. Keep moving with Dash Through and stay under the ledge as much as possible, and it's not too hard to take down the two Warriors.