I have come across a strange problem in one of our applications on win2k8/Vista x64 with UAC enabled. It is a process which hosts the UI for our service and runs in the context of the logged on user. When logged in as a domain user who is a member of the "Administrators" group, writing to the registry under HKLM fails due to UAC with access denied. But when logged in as the local "Administrator" account (non-domain) then writing to the registry succeeds. Both accounts are adminstrators - is there a distinction between domain and non-domain accounts with UAC? What gives?