The problem has been solved after I luckily noticed a seemingly unrelated post on microsoft.public.sqlserver.odbc . Through some combination of installing, uninstalling and deleting files, a key had been created in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\ExceptionComponents blocking the proper reinstallation of the DLL. Deleting the keys related to SQL Server from that key hive allowed the reinstallation to fix the problem.