As you might know, ChemSage data-files come in ASCII, binary, and transparent flavors. Whereas ASCII data-files are portable between platforms and compilers, binary files are not. There is no Fortran standard with respect to binary files, the result is that a binary file created on one platform or compiler (e.g. with ChemSage or FACTWin) is in most cases not readable by ChemApp.
The more recent transparent data-file format achieves some kind of portability between various compilers on DOS/Windows platforms. Thus, a transparent data-file created with FactSage can be read by a ChemApp DLL for Visual Basic®, for instance. To learn more about transparent data-files, please consult the ChemApp documentation (-> ChemApp documentation light/regular). ChemApp light users: Please note that ChemApp light does not support transparent data-files yet.