Fail to edit theme footer

Please help me solve this, why every time I want to update Appearance >> Theme Editor >> Footer >> it always fails

(Something went wrong. Your change may not have been saved. Please try again. There is also a chance that you may need to manually fix and upload the file over FTP.)

• This topic was modified 5 years, 4 months ago by Yui. Reason: renamed topic, not informative name

The page I need help with: [log in to see the link]