I have completely uninstalled this latest version, restored all original files, manually removed the old geek article system (v3), renamed my admin folder to admincp, cmodded the gas folder (and all files and subdir's) to 777, and started the installation.
This time it was done in a few seconds and my messageboard continued to work, no errormessages and my forumdisplay.php?f=11 gave me a wonderfull new Geek Article System 3.5 layout.
On thing that seems odd: the layout of the forumdisplay is new (with the icons, etc.), but the article showthread is the same as I had edited it for the old version (changed the layout a bit), but this time the sidebar is missing (so no thumbnails, ratings, etc.). It seems like the old Geek templates haven't been fully updated?
I'm going to let the dog out, have a dinner and then enjoy your amazing work more

..... Thank you SO much.