Going for Gold - Willielmus not reacting

Submitting the following bug:

ISP:
Ciaway NL

Type of Internet Connection:
Fiber

Internet Connection Speed:
150 Mbps

Date & Time:
11/20/2013 From approximately 18.00 CET till current

Frequency:
On going

Character Name:
Xavie Danai

Race:
Race of your character when the issue occurred.
Elezen Wildwood Female

World:
Moogle

Class/Level:
Warrior Level 47

Area and Coordinates:
Coerthas Central Highlands X14, Y35 @Aurum Vale.

Party or Solo:
Solo.

NPC Name:
Willielmus.

Monster Name:
-

In-Game Time:
7.48 am Server time

Steps:
When finishing the quest "Going for Gold", the NPC Willielmus does not respond. It has the green quest finish icon above his head, but everytime I try to talk to him, the screen goes a bit dark for a split second and then nothing. NPC next to him I can talk to.


PC specs:
OS: Windows 8
Processor: Intel i5 - 4670 with Geforce(tm) GTS450 1.0GHz
RAM: 8.00GB
System Type: 64-bit Operating System, x64-based processor