tortoiseSVN: got error message when commit file

tortoiseSVN: got error message when commit file

I am using TortoiseSVN to commit a file. But I got bellow error message:
Error post-commit hook failed (exit code 25) with output:
Error An unexpected error has occured. The process at spawn ID exp5 has
produced the following output:
Error yes
Error
Error Failed to add the host to the list of known hosts
(/var/www/.ssh/known_hosts).
Error Password:
what does this mean? and how to fix it?