First of all: thanks for your reply and help.
Following are the versions of my apache2 and openssl:
Server version: Apache/2.2.14 (Ubuntu)
Server built: Nov 3 2011 03:29:23
OpenSSL 0.9.8k 25 Mar 2009
This versions should support SNI following http://en.wikipedia.org/wiki/Server_Name_Indication
So I just activate SSL on two different webs and SNI should work? (with a SNI capable browser of course)
Great, that was the solution! Thanks a lot Till..you saved my day, apache2 is running again
But why do I still get:
Warning: DocumentRoot [/var/www/[one_of_my_webs_SYMLINK]/web] does not exist
I deleted the concerning web2 a day ago via webpanel. I had no error message. Should I delete the still existing symlink in /var/www manually?