Unable to open arhcive file

For no real apparent reason, I start up my computer this evening and while GW is booting up, I get a message saying "Guild wars is unable to access it's archive file 'GW.dat'. Please verify that this file is accessible and writeable, and that no other program is currently using it."

I don't know what the hell to do, can anyone help?

Well, you might start by verifying that the file is accessible and writeable, and that no other program is currently using it.

The file should be in C:\Program Files\GUILD WARS\ if you installed in the default directory. If you changed the directory then you should know where it is. Verify that the file is not set to read only or something like that.

If your file isn't set to read only, what Elder said.

might be a corrupted gw.dat file - if that's the case you will need to re-install or run the -repair or maybe even -image command line...

If you're running Windows 7 or Vista make sure 'gw.exe' is set to "Run As Administrator" otherwise it won't have write access to the .dat file.

I just encountered this problem, and some- 1's solution worked.
Though why I was able to run gw.exe several times before this happened is a mystery to me.