If you receive this error from a server it could be one of these problems:
The site you are trying to log into requires a special user name and or password in order to transfer files.
Contact the administrator of the site, and find out if you need to be using a special user name or password, and whether or not you can access that site.
The permissions on the site are incorrect, so even though your user name and password are correct, you are unable to upload or download.
Contact the administrator of the site, and make sure that your user name and password have read and write permissions set correctly.
You cannot upload because the server you are sending to is full, and will not allow more files to be uploaded.
Delete files that are no longer used, or ask the administrator for more space on the system.
The file name you are using has a space or a character that the server will not allow.
Double-check with the administrator of your site about which characters are accepted on your server, and rename the files to an acceptable name.
A communication error is occurring between the FTP host and your computer, making data transfer impossible.
If Deva xFTP has worked in the past, change nothing and wait a little while to see if the problem is caused by Internet traffic.