Is a file corrupted or too large even ZIPed?
While they mention MS Visio (vsd vdx vsdx) as eligible format for WFA, there's a note:
If you received a VSD file, ask your client to save it as XML Drawing (*.vdx). As of Wordfast Pro v. 3.2, Visio (VDX) files can be translated directly just as any other supported file format without the need to write custom conversion rules. Use File menu > Open to open the file. When you finish translation, use File menu > Save Translated File to get the target file in the same *.vdx format.