How to downgrade from V9 to 8.305

Hello,

Basic question apparently....I spent many hours to try to find out my problem for this "normally" formal steps.

As we have issues with V9, I'm trying to downgrade to the previous version.

I found the file 8.305.iso on the ftp from Astaro and then I burned a CD.

But no chance to finalize the installation...after formatting the partition, the wizard told me :

• Bootstrap : Error: install.tar wasn't found on the installation media

I burned again 3 others CD and also tried to use a USB key but no success...

What is crazy is that this file is present on the media...but the process stop there...

Any ideas please ??? my situation becomes critic now and I have to downgrade now as soon as possible.

Thanks for your help