Despite the error message, the issue isn't 16-bit or 64-bit or 32-bit.
Screenwriter gives that error when the file you are trying to open is either not a Screenwriter document, such as a PDF file, or if the document has been damaged., like almost every other application, doesn't import PDF documents.
If the document file is damaged, here is a link describing how that might happen and how to recover previous versions:
Causes and solutions for damaged Screenwriter documents (.mmsw) on Windows
If you want to import from Microsoft Word, then you need to use Microsoft's RTF (Rich Text Format). You can also open your document in Word, select all text, copy and paste into Screenwriter. This can be effective, but depends on how consistent your Word document follows screenplay conventions.
Here is a link with directions for getting the contents of a PDF file into Movie Magic Screenwriter:
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