connection aborted by host software

[rogerfgay]

"An established connection was aborted by the software in your host machine."

I know I've solved this once before, but haven't used ftp in a while.
I am able to connect using a client program or in a command window (Microsoft ftp).
I have contacted support for a newly purchased client program, but they say they are unable to connect.

ftp isr.mine.nu
ftp 83.251.254.172

I fooled around with passive verses active settings at one time in the client ... but was trying other things as well, and don't remember whether that was the solution.
I have searched the forum and found 4 other threads with problem defined by the first statement in this post ... and either didn't understand them or didn't think they had much to do with my set-up.
I am running through a wireless router - but all this stuff worked before; even with the client I'm using now. (during the free trial period).