Although I have not tried to program this device, if I select the device it loads without the error message you reported. Try updating your software, from **broken link removed**
My version of the software may be more up to date than yours, as I understand it (I may be wrong) the software while being 4.20 comes in different stepping numbers. I think the version I have is the latest version. You can download it and try it (I also corrected many of the spelling errors) here,
I am sorry I made a mistake on the version number, I should have said 5.2 not 4.2.
The above link is the latest version of 5.2 with some spelling and grammar corrections, it works on my XP system with the sst27sf256 as far as loading the device goes, but I have not actually tried to program this devices as I do not have one.
it's always the same error message, it's very strange because i have no error with sst27sf512 for example.
i have the error without chip on the G540 too.
Sorry I have made yet another mistake, I tested the sst27sf256 WITHOUT the programmer connected and I did not get the error message, however when I connected the programmer I get the same error message as you. Another bug with the G540 software. You could try programming it as a sst27sf512, you will get an error message, but it may program correctly.