Error 'fatally failed' msg attempting FTP ing files

I transfer 10-20mb .flv files to a couple of my DH sub-domains several times a week, but lately I’ve been plagued with failed transfers. I’ve changed nothing in my procedures. I use WinSCP. Interestingly, when I transfer smaller files (under 1mb), there are no problems.
Here is the error msg:
Copying file ‘mycomputer/something.flv’ fatally failed.
Copying files to remote side failed.
Anybody had this problem and worked out how to fix it?

Please don’t double-post requests. I’ve already responded to this.