I have been debugging the problem for some time now.
I already swapped the motherboard for a different brand and type, swapped graphics card, bought a new power supply (450W), tested harddisks, tested RAM (Corsair twinx 2048 MB 3200C2) over and over with no solution. I ran memtest86+ for hours and hours without any errors.
GW crashes at least about every hour with the "serious error has occurred, please send a report to Anet". The system is not overclocked and completely stable in 2d.
I am using latest drivers, bios, defragged the harddisk, increased virtual memory size to 2048-4096.
Also checked overheating: graphics card / processor etc are not getting too hot.
The graphics card is an Asus EN7800GT. Processor is an AMD 3800+ X2.
More system info:
CPU(s)
Number of CPUs 2
CPU#1 APIC ID = 0
Name AMD Athlon 64 X2 3800+
Code Name Manchester
Specification AMD Athlon(tm) 64 X2 Dual Core Processor 3800+
Family / Model / Stepping F B 1
Extended Family / Model F 2B
Brand ID 5
Package Socket 939
Core Stepping BH-E4
Technology 90 nm
Supported Instructions Sets MMX, Extended MMX, 3DNow!, Extended 3DNow!, SSE, SSE2, SSE3, x86-64
CPU Clock Speed 2009.3 MHz
Clock multiplier x 10.0
HTT Bus Frequency 200.9 MHz
L1 Data Cache 64 KBytes, 2-way set associative, 64 Bytes line size
L1 Instruction Cache 64 KBytes, 2-way set associative, 64 Bytes line size
L2 Cache 512 KBytes, 16-way set associative, 64 Bytes line size
L2 Speed 2009.3 MHz (Full)
L2 Location On Chip
L2 Data Prefetch Logic yes
L2 Bus Width 128 bits
CPU#2 APIC ID = 1
Name AMD Athlon 64 X2 3800+
Code Name Manchester
Specification AMD Athlon(tm) 64 X2 Dual Core Processor 3800+
Family / Model / Stepping F B 1
Extended Family / Model F 2B
Brand ID 5
Package Socket 939
Core Stepping BH-E4
Technology 90 nm
Supported Instructions Sets MMX, Extended MMX, 3DNow!, Extended 3DNow!, SSE, SSE2, SSE3, x86-64
CPU Clock Speed 2009.3 MHz
Clock multiplier x 10.0
HTT Bus Frequency 200.9 MHz
L1 Data Cache 64 KBytes, 2-way set associative, 64 Bytes line size
L1 Instruction Cache 64 KBytes, 2-way set associative, 64 Bytes line size
L2 Cache 512 KBytes, 16-way set associative, 64 Bytes line size
L2 Speed 2009.3 MHz (Full)
L2 Location On Chip
L2 Data Prefetch Logic yes
L2 Bus Width 128 bits
Mainboard and chipset
Motherboard manufacturer DFI Corp,LTD
Motherboard model LP NF4 Series, 1.0
BIOS vendor Phoenix Technologies, LTD
BIOS revision 6.00 PG
BIOS release date 06/23/2005
Chipset nVidia nForce4 rev. A3
Southbridge nVidia nForce4 MCP rev. A3
Sensor chip ITE IT8712
Graphic Interface PCI-Express
PCI-E Link Width x16
PCI-E Max Link Width x16
Memory
DRAM Type DDR-SDRAM
DRAM Size 2048 MBytes
DRAM Frequency 200.9 MHz
FSB

CAS# Latency 2.0 clocks
RAS# to CAS# 3 clocks
RAS# Precharge 3 clocks
Cycle Time (TRAS) 6 clocks
Bank Cycle Time (TRC) 12 clocks
DRAM Idle Timer 256 clocks
Command Rate 1T
# of memory modules 2
Module 0 Corsair DDR PC3200 - 1024 MBytes
Module 1 Corsair DDR PC3200 - 1024 MBytes
Software
Windows version Microsoft Windows XP Professional Service Pack 2 (Build 2600)
DirectX version 9.0c
Has anyone got any idea how to fix this?