Here is what happened...
I was doing an update to CiviCRM (through the recommended process) from .10 to .15.
After I copied the files over, I was getting a 500.
So I checked the log and I was getting an error message:
Notice: Constant CIVICRM_MEMCACHE_PREFIX already defined in include_once() (line 310 of /home3/isrcus/public_html/sites/default/civicrm.settings.php).
and the next one:
Deprecated function: Methods with the same name as their class will not be constructors in a future version of PHP; backup_file has a deprecated constructor in require_once() (line 279 of /home3/isrcus/public_html/sites/all/modules/backup_migrate/backup_migrate.module).
Why am I getting those error messages?