Unable to save as a PDF

[Zac23816266xjdx]

Hi,

I am unable to save my work as PDF. Every time I try, the file saves a PDF with the following message on a white background.

"This is an Adobe® Illustrator® File that was saved without PDF Content.
To Place or open this file in other applications, it should be re-saved from Adobe Illustrator with the "Create PDF Compatible File" option turned on. This option is in the Illustrator Native Format Options dialog box, which appears when saving an Adobe Illustrator file using the Save As command."

I have made sure to check the "Create PDF Compatible File" box when saving the file as an AI file prior to saving the PDF, but am still getting the same message. I have also tried starting a new file and dragging all of the objects from the original work to the new artboard, as per the instructions given to someone else with the same problem on a different thread, with no luck. 

I have saved loads of works as PDFs in the past with no issue, does anyone have any ideas?

Thanks

[Ton Frederiks]

Things like restarting your machine/Illustrator may help.

If not, try to reset Preferences:

https://helpx.adobe.com/illustrator/using/setting-preferences.html