This problem has started occuring just this evening.

Everytime I try to upload a file that already exists on the server (such as index.php), I get an error:

STATUS:> Connecting data socket...
550 index.php: Overwrite permission denied
ERROR:> File error
STATUS:> Failed to send c:\web\humor\index.php
This is in CuteFTP. I get the same thing in command prompt FTP.

However, if I upload a file to the server that doesn't already exist, it'll get uploaded.

What could be the problem? How do I rectify it?