drush cc all giving me an unlink error
I've seen this problem when as unprivileged user you call drush cc all and drush tries to delete cache files created by the web server process. Those files are owned by the web server user and they don't have the 'all other users" write permissions enabled (the last three permissions group).

Fixing this is a file permissions issue. One fix is to put web server user and drush user in the same group and assure that files created by the web server process are writable by its group members.