This is a Windows system installed file with Windows File Protection (WFP) enabled.
cscui.dll has 47 known versions, the most recent one is 6.1.7600.16385 (win7_rtm.090713-1255). It adds a context menu to the Window's shell named Offline Files. The average file size is about 1.36 MB.
(Note, the behaviors below are for all versions of cscui.dll, select a unique version for details.)
Located in the registry at 'SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Approved'
United States installs about 46.58% of Client Side Caching UI.