After upgrading to 5.1 I had this error crop up with a couple of documents. Here is one of them:
[Appending Task Documents] Last File = C:\Inetpub\wwwroot\secure_consultationconnection_com\SafetyWriter_v2\IndividualSafetyInstructions\sp\Remoción de paredes y pisos-Removal of Walls and Floors.doc [ Aspose.Words.UnsupportedFileFormatException: Unknown file format.
at Aspose.Words.Document.?(Stream ?, LoadFormat ?, String ?)
at Aspose.Words.Document…ctor(String fileName, LoadFormat loadFormat, String password)
at Aspose.Words.Document…ctor(String fileName)
I’ve attached the file. If it helps I think the lady who created these originally created them in docx, but I had her resave this to doc, but there may be some wierdness in it.