Found this somewhere else, and it worked for me (Windows 8 – 64bit – Enterprise)
Try this
locate the gw2.tmp file (it size should be around 10 Mb (in my case it was 0MB)). Make a copy of your exe, and rename the tmp file to exe.
So:
Gw2.exe → Gw2copy.exe
Gw2.tmp --- Gw2.exe
and open Gw2copy.exe .