Fireworks not saving preferences

Hello,

I am using Fireworks CS6.  Earlier this week it started to revert back to original default preferences every time I restart computer, sometimes just when I restart software.  Previously preferences were retained without problem.  This is a significant nuisance as I am a designer using the software all the time and I now have to change preferences at least once every day - especially tedious since some, such as max canvas size,  have to be manually set in preferences file itself.

Doers anyone know why this might have suddenly started happening?  I am running Windows 10, fully up to date.

Thank you.