Mif2go - suddenly some graphics files won't import when creating HTML

[Susan OConnor]

Hi Everyone,
I'm suddenly having a problem with Mif2go. All of a sudden graphics files
have stopped importing on some book files when I'm creating a HTML file.
Others import just fine. The graphics files are in the same folder, have
the same format - I can't find a difference between them that would cause
this behavior.
I've tried embedding the files instead of referencing them, but that
doesn't help.
Has anyone encountered this problem before?
Thanks,
Susan O'Connor