Database backup error

Backup database from admin panel get this error.

Any suggestion for this error.

Thanks

File does not exist: /home/mysite/public_html/500.shtml,

referer: http://mysite.com/administration/db.php

The 500 error means "denied" which is normally:

1.  A permissions problem

2. You're being blocked by the htacess.

3. You're being blocked by security software like mod_security

For some reason your server is trying to load an error message template from your local directory. That's why you're getting a file not found on the 500.shtml. 

That doesn't make sense to me. why would a database backup create this type of error.