As in the description, I can make an SSH connection to the host and I can copy files off the host to my own computer with SFTP, but I can't copy files to the host with SFTP.
Other users on this host can copy files both to and from the host with SFTP, and I've tried using different computers and different SSH/SFTP client software to connect to the server; none of them work. I've checked my disk quota to make sure I have adequate space for new files. So as far as I can tell, this problem seems to be strictly user-specific.
What can be causing this problem?