[squid-users] problem with authentication

Hi list,

i've followed this guide (semi) successfully:
http://wiki.squid-cache.org/ConfigExamples/Authenticate/WindowsActiveDirectory
All seems to work (dns resolution, ntp, wbinfo), but Internet Explorer on the clients bring an authentication window. But a) it doesn't accept any credentials and b) it don't want this windows at all .
Can somebody give me a hint?

Proxy:
CentOS 6.3 x64
Squid  3.1.10

ADS:
Windows Server 2008 R2

Clients:
Windows 7
Windows Terminalserver 2003

Thanks for help

--
Marcel