authentication to webproxy fails using wpad and autodetection, but works fine if proxy is set in the browser

Hello,

some of the clients have trouble with internet access over the TMG. The IE is configured to use wpad, which is setup as an DHCP option. In the logs I can see, that the clients are not authenticated. If I enter the proxy parameters in the browser settings, everything works fine.

Has anybody an idea, what may be wrong?

Regards
Andreas