I'm using Windows 7, also I think I've possibly twigged the problem, and it's bloody weird. Although you are correct about it occurring across versions. In MO, I was using a working profile Fear and Loathing - I re-installed an older version of MO and tried running the 4GB loader, and it worked fine. I then went ahead and made my new profile to begin modding in earnest and tried again - and it crashed. Back to default profile, works again. Have recreated this on both 1.3.11 and 1.3.8, so I guess I just have to keep my modding to the Default profile in MO? This seems like an odd problem considering that the F&L profile is new and thus, presumably, the same as the default profile when it isn't working. Anyhow, hopefully that's it.