Damnit, just when I redo the entire stout mines to get the Assassin dagger, I equip it on my rogue, enter the Pawn Shop, and find that NOTHING happens! The stupid Bratsol guy tells me the usual "you haven't lowered the drawbridge" "you haven't found the Arbidren books" blah blah blah :(
From what I've read, you only have to equip the dagger and enter the pawnshop with it to become an assassin, so what am I doing wrong? I am SO sick of running around with a crappy Rogue who does 6 damage per attack, and I just can't wait for him to become a real character. Any help would be appreciated, thanks!

Are you sure you've selected your rogue when you enter the Pawn Shop?

Try having your rogue selected as Neb suggested and just have the dagger in your inventory, not equipped.
Let us know if these help, we'll try to come up with more solutions!

Hooray, I figured it out! The conflict was due to the fact that I still had the Ninja quest waiting to be completed. I guess this causes a conflict with quest assignment, and you cannot be upgraded to an Assassin while still waiting to switch to another class. This is probably a decent discovery for future players, who can avoid the frustration I encounted. Thanks again!