Using New Data Types in Your IDL File
The Basetsd.h header file defines the new data types needed for writing applications that run on both 32- and 64-bit Windows. To use these data types in your interfaces, import Basetsd.h into your IDL file. Do not #include the file or you will end up with multiple definitions at compile time.
Alternatively, you can include or import the Basetsd.idl file into your IDL file.