Obj Export Suddenly failing

Without any change to the computer or to the WIP, Suddenly the Obj export is failing. Both via the usual macro I always use, and manually though the export command.
I get this:
Failed to save as /Users/akash/Documents/Zbrush Work/FromRhino.obj.
The file writing plug-in failed.

This all works as usual in R7.

thanks a lot

My guess is Dropbox had locked the folder to sync files at the time.

Interesting, thank you,
it is back to working correctly now, so that may well have been the culprit.
Even though… I did do a computer restart at the time and still had the problem hours later…?
thanks a lot