Ok I had no problems with install or download. The game launched and runs fine and so far I love it. BUT I cannot get out of the "Barricade " mission in the prologue. I went into the town and found the tunnel to get into the abbey yard and open the gates for king etc. I crossed the bridge and lost the Dragon no problems.

But once I got on the walls of the seige equipment and then had to jump down to the yard to fire ballista my troubles began. I have tried to aim that dog gone thing at least 1000 times (tried starting game over and finally tried re-installing) but there seems to be a glitch with that bar filling up all the way but then more of the same two groups of enemy soldiers attack and it's rinse and repeat. Seriuously I got a whiole level just on fighting these neverending balista guards. Does anyone know how to get around this or what I am doing wrong>?

AMMENDED:

I tried all of your suggestions, turned the mouse sensitivity all the way up, and it didnt work.
Then I tried once more this time i used both hands to tick my LMB and still no go...(more soldiers attacked) but when i went to try a third time it said "launch bolt" instead of aim. SO IT WWORKED THX FOR ALL YER HELPS! BTW I bugged it via email to cd projekt and they replied almost immeadiately and asked for a saved game , so they are gonna try to fix it. I like these folks...they may not have it all there now but they are tryin hard and will do so soon i think.
Thank you in advance.

This is either the third of fourth time I've heard of this exact bug. No fixes that I've heard of thus far, but I would definitely send an email to the developers and post something on their forums once they're back up so that they have a better idea of what to patch out. There's a patch that's supposed to be coming out fairly soon that fixes a bunch of known bugs, though whether or not this particular case is considered a known bug is left up to speculation at this point.

Sorry I couldn't be more helpful.

If you don't mind cheating (in your own mind a little) re-boot to clear the cache and restart in ez mode?? I think that will work!!

I have also heard of this glitch.

I believe someone got past it by reducing the resolution of their game by a notch.

If you usually play on 1920x1080, for example, try setting the resolution down to 1600x900, to pass this sequence, and increase it again after.

EDIT : Found the post that I was thinking of :

http://www.gog.com/en/forum/the_witcher_2/can_they_make_qte_worse

I haven't had a problem with most of the QTEs, but THANK YOU for suggesting this, I no longer suck at arm wrestling!!!

I'd dropped the mouse sensitivity down to make it easier to target dropped loot and containers, and I thought the arm wrestling must just be really really difficult (and it was making me feel stupid that I couldn't seem to do it!!) until I whacked the mouse sensitivity right up to max based on your post - just won my first match without breaking a sweat - off to find some more opponents now... :D