Hi! First I'd like to say a big thank you, FanficFare is the reason I'm using Calibre in the first place. I love it.
I've been having a problem on and off for a few months now, when trying to add or update a story from fanfiction.net.
I always get an error message of that type:
'utf8' codec can't decode byte 0x92 in position 44: invalid start byte
https://www.fanfiction.net/s/5536346/1/
It's always been "can't decode byte <something>" and "invalid start byte". I have looked for other case of these error messages popping up, but I've never found anything similar.
When it happens, every fanfic I try to download just fails (note that if a fanfic doesn't need to be updated, there's no problem, it only happens when it actually tries to download). The first time it happened it lasted for several days until I gave up, but coming back a few weeks later it worked once more.
Of course I always made sure to update both the plug-in and Calibre, but that had no effect. It took me a long while to discover that the problem was that the plugin was being blocked by my firewall (I use TinyWall). For some reason, despite allowing Calibre access to the internet (to download plugins and such), it can cause these issues with FanFicFare.
In order to let it work through the firewall (rather than just shutting down the firewall to update my fics) I applied the white-list to the process started by the Calibre job of running FanFicFare (just white-listing the executable for Calibre wasn't enough).
So I think that's about it. After spending hours scouring the internet in general and this thread in particular looking for people who had the same problem as me, I thought I'd share what I learned to spare someone else the grief.
Also, I thought it was a good occasion to express my gratitude for FanFicFare!