I got some problems after playing this map:
I am not able to talk to Shawford Crale(I get the talk icon, but when I click him he doesn't say a word, and no dialog screen apears)
when I try to talk to lord Ulbrec, I can't tell him that the bridge has been cleared of enemy's.
things that I could have done wrong:
killed Xuki before killing ogres(the bridge is now destroyed)
charmed highland snake(the one at the bridge and the one at the ford) and the charm spell stays active(I charmed one of those big cats and the spell expired shortly after, but the snakes stay charmed)
I can't really go back to a previous save game as my previous save game is quite far back

OK, killing Xuki 1st is no problem, I have finished game 2X each(killing her 1st or not). So this is not the problem.
Charming the monsters might be. You need to kill all the monsters on the screen, then you get XP for clearing the map. Check your journal, you should she a note saying you defeated all the enemies, but in your case, you couldn't save the bridge. if not go back to the map and hunt down that snake!
You should have an autosave before you reach this map, it is one of the toughest fights in the game. Check the autosaves for a place to go back. Also, from here forward, save at the end of each map. There are several spots where you change maps and are immediately jumped before you can prebull or summon help.

Once I let the bridge be destroyed because she said she could arrange a meeting with the Leigion for me. I don't remember the actual sequence of dialouge up to there, but if you say from there

1) "And do you have it within your power to arrange such a meeting?"

then the bridge will be destroyed because you hesitated in the effort to destroy it (you'll get a message saying this at the bottom of the screen.) Just thought I would mention this.

I think General Ghoul might be right. I've never had this problem but I have also never charmed a snake. I have failed to save the bridge plenty of times but I still got to go back to town and tell them of my failure.

it worked out, I got rid of the snake and after that everything worked

FWIW, I don't find the Shaengarne fight to be all that hard... I run to Xuki, have someone keep her busy, and have everyone else go after the Ogres.

I just kill everyone up to the Ogres, including Xuxi. Then finish off the ogres,
I like when your evil, that if you kill the villagers from Torak's section, they are there at the bridge as undead. Then with an evil cleric, you then take control of the undead. Makes the fight real easy.

Heck, that's just one of many reasons I like the Dreadmaster of Bane so much. In my last game I had a Dreadmaster of Bane as well as a fighter who dual-classed to Morninglord of Lathander. (Imagine the roleplaying convolutions needed to get them into the same party.) They absolutely blasted their way through the Kuldahar Valley: the Dreadmaster cowed and dominated half the undead and the Morninglord wrapped the survivors in fire.