long long wasn't added to visual studio until 2003 .NET. Therefore, visual studio 6 is not functionally able to work with long long using that IDE. http://msdn.microsoft.com/en-us/library/aa983524(VS.71).aspx "The long long type is now available as a typedef of __int64. See Fundamental Types for more information. Note that there is not yet support for long long in the CRT." As for your DirectX libraries, are you sure you have correct one installed for the app you are developing. Maybe you are one version behind? Either that or your libraries are not where your path is expecting them to be. As some of the previous posters said, move up to a more recent version of Visual Studio. After installing 2005/2008 reinstall your DX SDK.