We are using EAP-PEAP, ACS 4.1, Windows2003SP2 (Active Directory).
The problem is that wlan clients are not authentication with EAP-PEAP.
The logs on ACS display "internal error"
the internal DB on ACS works fine, but not interacting with windos2003 AD.
Make sure the ACS is part of the domian and that ACS has your windows doiman connected and showing in the group mapping.
I've the same problem.