Thanks for your help guys, I really appreciate it.
Luckily, I didn't need to download a bloody thing, since I had already downloaded the latest ToB patch some time ago. It had been so long since I played BG2, I totally forgot that I had the patch! I only just discovered it while I was going through My Documents folder!
The reason behind the bug was due to the fact that I have Win XP as my OS. Yep, an ol' XP compatibility issue of all things. The patch I had easily fixed this, and I didn't even have to start a new game. I reinstalled the Ascension WeiDu mod, just in case I lost any of the mod's features (although I won't be able to tell until I reach the ToB quests).