Dear Leslie, dear Skandha,
thanks for your support. I tried the steps Skandha has listed when first trying to upgrade. I now installed the catch updater as Leslie suggested and closely followed the steps described in Catch Themes video tutorial for the updater but with the same result: The whole page has gone blank. What I noticed though: When going to the Themes-page the name of the active theme is not displayed. There is just three dots where the name should be. I am totally out of ideas now…
Bst rgds
Carsten