20 12 2012
Unable to resolve NTLM or Windows users in People Picker in Central Admin
This totally drove me round the bend.
If you’re in Central Administration and you can resolve FBA accounts find but not NTLM, then check to make sure you’re on the correct Alternate Access Mapping for the site.
You might be using http://centraladmin.mydomain.local:12345 and it may not work, until you access Central Admin via http://centraladmin:12345.
Also, if you have a Claims-aware web application with both FBA and NTLM memberships (extended or not) and you have broken the configuration for FBA, this may also break NTLM resolution of names. Make sure you have the Membership provider delcared properly in Central Admin, the Secure Token Service and the target web application.