That's strange. I was able to run about thirty instances without getting any error.
Anyway I'll try some improvements and will sent you new version.

Is it possible to increase the number of concurrent sessions WINSCP can support when running scripted sessions using winscp.com? Each session talks to a different server.

I get the error message "Cannot find unique name for event object" when I try and run more than 5 at once.

I know I'm abusing the product, but the application has to run over a slow (56Kbps) cellular wireless network, so running sessions in parallel is the only way to get a download to all servers in a reasonable time.