434 is patching error, can be caused by many things
-anti-virus (Avast especially)
-patch file folder corrupted - PSO2 download the patch in a temporary folder and removes itself after installing. I don't exactly know where it is located - but if you can find it, delete it and try to patch again.
other things i found digging around is that it is an old tweaker problem with permission settings - it should have been fixed though.
Also if you can make it to the menu of the JP launcher, do the file check/file repair - it can fix some corrupted files
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