How can I change the format of an unrecognizable FrameMaker file? Why did it become unrecognizable after I changed the file name?

[Perennial_Writer]

I am updating an existing FrameMaker10 project, which is in a book structure.  I have changed the names of the files in the directory, updated them to FrameMaker 11, and saved them.  When I try to add them back to the book (whose name I have also updated) a problem occurs for some of the files. When I try t add them to the book file, I get an error message which says that the book file is unrecognizable.  (It does allow me to add it, but it appears in the book file with an icon that has a blue "M" in it.)  Why is this happening and how can I change these files back to normal FrameMaker files?  Thank you.

[Arnis_Gubins · Accepted solution]

Try opening the problem files using a text editor or file viewer to see what the first few bytes contain. All valid FM binary files for FM 11 will contain <MakerFile 11.0> in the first bytes of the file.

When updating books, it's sometimes better to just to create a new book file and add the files to that.

When renaming files in a book, changes at the system level will break any links/cross-references between files, so it's always best to use the Rename option in the Book file to change FM file names. This will maintain the correct linkages.