You start the day with a job you had pending from the previous day and I find that it fails Filezilla .. makes you want to go back to bed

Luckily the solution was quick and I could continue what was pending and lost time.

What is the solution for error 421 too many connections?

Well, if you use cPanel you have to interrupt the FTP session from FTP Control session

Then open FILEZILLA and modified transfer options, select the option limit the number of simultaneous connections

Problem solved! for me ;). I wait this tutorial help you