So what happened is: As of yesterday GW2 will now detect what architecture you are running (64, 32 bit) and will start accordingly. Midnight only supports 32 bit right now though. Here's what you have to do:
1) Locate your GW2.exe
2) Create a shortcut to it
3) Go to properties and add a "-32" to the launch parameters, it'll look like this:
Code:
D:\Games\Guild Wars 2\Gw2.exe" -32
4) Always use this shortcut to start GW2, it forces it to start in 32 bit mode no matter what.
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#updated