Hacking Wordpress skill assesment

I have basically finished this module save for the last part. I have gotten access to the Erika account and am attempting to upload a shell to the template for 404. however I keep getting this error:

Unable to communicate back with site to check for fatal errors, so the PHP change was reverted. You will need to upload your PHP file change by some other means, such as by using SFTP.

Is there some other path I am missing or is this a technical issue? Thanks for any help.