Linux – SVN post-commit update error (Can’t create temporary file from template / permission denied)

My post-commit hook is:

/usr/bin/svn update /var/www/html/mysite/ –username myusername –password mypassword –no-auth-cache >> /var/www/html/mysite/foo.txt 2>&1

After performing a commit, my post-commit hook outputs to foo.txt the following:

Updating '/var/www/html/mysite':
svn: E000013: Can't create temporary file from template '/var/www/html/mysite/.svn/tmp/svn-XXXXXX': Permission denied

Any ideas?? Must be something related to permissions. It used to work, but something happened.