Did you use forbidden characters like /, \, | and some others in your file, path or folder name?
Are all files on an active network drive?
Are all files closed and not used with another application?
Do you have copy permission for all files?
Yes ( I just closed everything down and reopened the packaged file - same message)
It is a template that I have been using for over 12 months. It's only been in the last week that I noticed the error message. I just add 4 new photos as stock changes and update the description.
I had 2 hidden layers and just checked that they don't have anything missing, but again - no error messages within the document or links panel.
Does the preflight indicate which link is problematic?
Did you try to export as IDML and reopen the IDML, save as new INDD and package from here?
Could you investigate in your IDML file if something got corrupted? Open the IDML in some kind of XML editor like BBedit or OXYGEN and look if some hidden content is making problems.
Or make a copy of your file, delete everything visible. Try to package.
If the problem still exists, delete one page after the other and always try to package until you get to the problematic page.
If there is still a problem, then export an IDML and investigate this as described above, now it should be easier to find the problem.
Is there something on the pasteboard or a hidden layer? The package command does not include hidden or off-page content in the package.
But this should be visible at least in the link panel.
That's true, but the same would also be the case for a file that was not packaged due to an invalid character.
I wonder if it might be a link nested in another link, like an illustrator file or a placed page from another ID file.