Just started using Audacity, converting vinyl to digital files. Using Mac OSX Mojave 10.14.5, Audacity 2.3.2. I have had great success exporting and saving files as AIFF, until something happened when I was editing labels. The next new .aup file I tried to export and save as an aiff format generated this message. What can I do to correct this problem? I reset Audacity to factory settings to no avail; deleted and installed a fresh download of Audacity, and got the same message when I tried exporting and saving a new file. I suspect this is a cache problem, but I am at a loss as to where I locate and delete the errant cache.
Many thanks in advance for your help! 
Problem solved - of all the dumbheaded, amateur mistakes to make, and not see!