[Q] "DPInst.exe does not execute on your current o.sys" error when using FlashTool topic

I have an Xperia Tablet Z (SGP321) running stock 4.3 _10.4.1.B.0.101, and have been trying for the past week (on and off) to downgrade the firmware to 4.1.2_in order to obtain root, and re-reflash 4.3

I have tried EVERYTHING, but no matter what I do I keep getting "DPInst.exe does not execute on your current operating system" error message.

I've scoured XDA and other sites regarding the issue but, to be quite honest, ended up as confused as a bag of cats!!!

No disrespect to contributors - who I know do this for the love of Android, and from whom I (and thousands of others)have benefited enormously - but some of you really need to learn how to write clearly about how you've achieved route, flashed roms etc.

For example, posts like "I downgraded to 4.1.2, rooted, and re-flashed to 4.3 without any problems"" doesnt help anyone!! and comes across, to me anyway, as smug.

Anyhoo, I've used alll versions of Flashtool from 0.9.11.0 to 0.9.15 - no joy;

DESPERATE for help as I cant stand using an un-rooted android device (pop up adds all over the place; can't create my own hosts file; no xposed framework/modules.....all of this is my idea of Android Purgatory...but with none of the laughs!!!! or, worse still, an iPhone(y)

Thanks in advance

I'm running Windows 7 Ultimate 64bit