Okay I downloaded gwdatbroswer to browze the Gw.dat file. Anyways, these are the error messages I get when clicking on it. I extracted it in C:\Program Files\Guild Wars\
Sorry to revive an old thread but I'm also having this same problem and I've tried everything mentioned in this thread but still can't get it to work.
I've googled and this is the only relevent place I could find. I've tried opening GWDatBrowser on both of my computers, but ironically I'm getting the exact same error. I don't have a clue what to do, hopefully somebody can help.