Ok a few questions for you
1. what OS you running (xp/vista etc)
2. where is the datfile located - eg in gw main directory
3. Is the datfile protected - rightclick it and see its properties
3.1 Unsure if this applies but do you have admin rights to change dat files setting in above.
Off top of my head - -repair many of us woulkd say dont use , it tends to try and repair the datfile and from my own experience of -repair its shite at doing it.Ive spent an hr before watching gw try and repair its datfile then when restarted it repairs again.
This is the important bit - find the datfile and delete it - yes delete it.
Make a shortcut copy of gw shortcut ( on desktop ) and name it image
Ensure that its a shortcut
Then rightclick the image shortcut and at the end after the gw.exe" add a space then -image.
It should read towards the end .... gw.exe" -image ( remember between the " and - is a space )
Then run the image shortcut - probably best before bed as it takes a while
Finally if you have either a rw dvd or space on hd make a copy of the datfile and keep it safe.This saves a lot of time having to reload datfile and so far even on 2 new computers ive never had to download the whole datfile.
Damn this is becoming a wall of text.
-image i feel is better because it does a fresh datfile rather than try and patch up the old one which may be too bad to recover.