Hmph.
Pinpointing gwx2 errors is an inexact science at best, but let's eliminate a few possibilities. Apologies if any of these questions seem obvious to you
#1 You have two separate directories on your hard drive, both of which contain identical copies of both gw.exe and gw.dat
#2 Let's use the example that these two directories are both in C:\Program Files\ and are called
Guild Wars and
Guild Warz. Your paths in gwx2 should look like this: