I am trying to fix this problem in fzero gx. I am getting this unknown opcode crash frequently. I notice it seems to mainly happen during races, especially on diamond cup maps. After it shows the unknown opcode it also displays this other message which says illegal command 3f.

Here is what both error messages say:

GFX FiFo:Unknown opcode (0x3f)

This means the following:
Emulator got desynced
command stream corrupted by some spurious memory bug
This really is an unknown opcode
some other bug

illegal command 3f

cpBase: 0x0155b000
cpend: 0x0161afe0
cpHiwatermark: 0x000bc000
cplowatermark: 0x00060000
cpreadwritedistance: 0x000275c0
cpwritepointer: 0x0156a300
cpreadointer: 0x01602d40
cpbreakpoint: 0x00000000
bff_gpreadenable: true
bff_bpenable: false
bff_bpint: false
bff_breakpoint: false

My computer specs:

graphics card is nvidia geforce gts 450
cpu is amd fx 4100 4 cpus 3.6 ghz
ram is 4gb
operating system is windows 7 64 bit.

computer is using dolphin 4.0.2
my audio backend is open al
my backend for graphics direct3d11