Unable, Full Disk?
It's server issue, wait few hours or talk with your hosting.
I thot that at first, but my site has a lame little web upload utility, and i can upload file through that fine, so I think it must be the smart FTP
No, it most likely is not SmartFTP. The FTP server might have quotas enabled that do not apply when using the web upload utility. The message "553 Disk full - please upload later" directly comes from the server, SmartFTP just displays it as-is.
you're right. i talked to them. they are fixin it.. thanks