What I'm saying is .. there's no way, just from that message, to determine what the exact reason was for disconnecting.
What I will say (and my assumption is that you are trying to FTP a document to some Resource) is that, setting up your Resource to perform Retries with a Delay will usually keep these types of issues from happening.
On your CONNECTION Tab inside your FTP Resource, change your Retries to 5 and your Retry Interval to 20 or 30 or even 60. This means, when you get that error, it will wait "x" time then try again, picking up where it left off. If (after 5 retries) you're still having an issue during transfer, then there will be logged information in your Job Log that will give you more reasons as to why .. if you have the "DEBUG" enabled on the FTP Task you are executing.