Download messages of corrupted files

I have had a few complaints now about download problems. This is the message that is coming up.

Warning: MarketPress was unable to download the file http://www.domainname.com/downloads/filename.zip for serving as download: Failed to write request to temporary file. in /home/servername/domainname.com/wp-content/plugins/marketpress/marketpress.php on line 3864

So clients are getting corrupted file messages. Can anyone tell me what this is and how to fix?

Thanks,
Brandee