Network error: Software caused connection abort

I am using the current version of WinSCP, and running it on two machines.
I have three different FTP sites that I log into.
On one machine, all three log in fine.
On the other, I get the error mentioned in this subject line, but for just one of the sites. The other two work just fine.
I have studied all of the settings in the advanced options and they are identical on both machines.
I am using SFTP, Allow SCP fallback.
Thanks for any advice.

Gordon Peery

Have you checked log file of the SSH server, comparing entries for log-in's from the two machines?