Slitherine

...So I've just downloaded the GS3 update, unzipped it, run it, asks for serial number. I insert it, response is "Invalid Serial number". My HDD crashed a few weeks back so in order to re-install CEAW I had to go back to CEAW Gold and get my serial number from Slitherine, so I KNOW it's valid cos I'm running GS2. What do I need to do to get GS3 installed if it doesn't like my serial number please?

That's odd, I installed CEAW gold fresh and then GS 3.0 over the top of it just recently and it accepted my serial number fine. I had some problems installing in in c:\program files (x86), permissions I think, but it works fine when I install it elsewhere e.g. c:\matrix

Maybe try deleting it and re-installing?

Are you installing with the correct version. If you have a Slitherine serial number you need the Slitherine version of GS v3.0 instead of the Matrixgames version. And vice versa.

I do have the same Problem.
Bougth the "Commander - Europe at War Gold - - old PC Promo Download" Version of the game this week (via Slitherine) and it installed without Problems, including the GS 2.0.
I've downloaded the GS 3 from here: patches-scrolls.de/bonus/975/58945/58946/download <- found that link in this Forum!
I've tried to install twice (with and without GS 2 installed) but no luck with my Serial.

You need to download from the Slitherine website and not the one you used.

It is confusing till the end! I've found a Version that seems to work, as it at least accepted my Serial. I found it on the Matrix-Homepage...