"The save failed due to out of memory or disk space".

I had a friend come over with her new Mac because when writing a thesis Word (2007?) claimed "The save failed due to out of memory or disk space". Given that the disk had more space left over than mine ever had (>200Gb), something else had to be wrong. Different Volumes didn't do the trick, permissions were ok, the folder wasn't dangling.

Turns out she used a feature from the equation editor that was incompatible with the .doc format and would have needed to save as .docx. Way to go Microsoft - I hereby proclaim you most useless and moronic error message producer of this month.