FEC errors mean that interleaving is enabled on your line and that it is doing its job, basically an FEC error means that any bad/corrupted data on it ways to you has been fixed at your end thus negating the need to re-transmit the info, by the looks of it if it was'nt enabled on your line then every single one of your downloads would end up corrupted or would take much longer to download.
You could maybe try rebooting your router to see if the number of errors lowers, as I had that happen to me ages ago when interleaving got enabled on my line for no reason, I got millions of errors/fixes and I rebooted the router and it settled down to a few hundred.
Also, interleaving gets enabled on lines that are having problems, or if you didnt specify that you wanted it turned off when you signed up with zen then I think its enabled automatically ? but since you are getting millions of errors/fixes then maybe you should call Zen to see if there is any type of fault in your line, especially if this just happened out of the blue.
Bottom line is, since you have interleaving enabled on your line then
those FEC ( Forward Error Correction ) errors/fixes are absolutely
nothing to worry about aslong as you dont have any other problems
related to your internet connection.