Hello all,
just had the same problem with an older zentyal installation. Solution is quite simple - just takes a little time to find out what is going on.
Updating zentyal-core from 3.2.19 to 3.2.20 installs a changed /usr/share/zentyal/www/default.theme which is missing some needed attributes: remote_svcs_bg_color and remote_svcs_hover_bg_color.
It seems to work when adding the following lines in /usr/share/zentyal/www/default.theme:
remote_svcs_bg_color: "#BBE03A"
remote_svcs_hover_bg_color: "#CCE86C"
I put the above lines after
hmenu_bg_color: "#46962D"
hmenu_hover_bg_color: "#69BE28"
This was quite quick and dirty and I did not test very much, but at least webadmin starts again.
Best regards
Ralf