Hi,
Ok I got it to work now.
You′re right. There was indeed no such css file. I re-installed the plugin again and when I activated it I got the following error:
Warning: fopen(………/wp-content/plugins/ajax-event-calendar/css/cat_colors.css) [function.fopen]: failed to open stream: Permission denied in ………./wp-content/plugins/ajax-event-calendar/ajax-event-calendar.php on line 1159
cannot open file
I guess that prevented the css file from being created.
However, even with all permissions set to 777 and creating cat_colors.css manually it still didn′t work.
So I re-installed it again (third time) and changed the permissions to CHMOD777 BEFORE activating your plugin. Only then the css file could be created automatically.
I′m not php nor server-stuff-savy but since it′s the very first plugin to ever do that I′m still not sure that it has something to do with any general faulty permission setting on my server.
Anyway…thanks for pointing me in the right direction.