It's not related to hard disk space.
It could be that you've had InDesign open too long - closing InDesign and reopen it and it could fix the problem.
It could be the internal structure of the InDesign file itself - so you could File>Export and choose IDML from the options (think it's File Save AS in newer versions?)
This can clear out unnecessary build up of code that is causing this error.
But if you let us know more about your issue and what happens and the exact error message.
Restarting seems to solve the problem but I'll try file>export>IDML as
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