Thank you! It works! Thats great. Interestingly neither authentication mechanism worked alone. I had to add
auth_param basic credentialsttl 2 hours before the basic authentication mechanism worked. The ntlm authentication isn`t working at all in my case. Therefore I think its a bit strange that I was able to authenticate before, by cancelling the first window and using the second window(the basic authentification). It also occurred to me that I had to do a /etc/init.d/squid restart in order to apply my new configuration. A simple squid -k reconfigure wasn't enough. Luckily it works now! You were absolutly right about the two authentication mechanisms. Thank you!
