read only in Frame 6

[Michael Wiesenberg]

What would cause one file in a book (FM6) to suddenly become read 
only, and, more important, how do I change it back again to 
modifiable? I can't save the file as anything modifiable. For any 
other file in the book, the File menu presents a "Save as" option, 
but not this one. When I look at the file's properties in Windows 
Explorer, "Read-only" is not checked. The backup file is in the same 
anomalous state. Windows Explorer shows no recovery or crash files. 
Possibly related information: Recently I got a "FrameMaker must quit" 
alert and FM died. The anomalous state of this one file occurred 
sometime after that.