Unsupported Operand Type when accessing /admin/content/simplenews

I get the following error when trying to access /admin/content/simplenews and /admin/settings/simplenews:
"Fatal error: Unsupported operand types in /path/to/mysite/modules/system/system.module on line 635"
It's a white screen except for the error.

I get all of my site templating and features back on those pages if I comment out this out in the system.module...

  if (!isset($item['mlid'])) {
    $item += db_fetch_array(db_query("SELECT mlid, menu_name FROM {menu_links} ml WHERE ml.router_path = '%s' AND module = 'system'", $item['path']));
  }

...but, after I comment that out, for those same two Simplenews admin paths I get this message: "You do not have any administrative items." (Even though there are newsletters sent and set up).

All the rest of Simplenews' features function normally, even w/o the hacked code. Also, all other modules' administrative features are functioning normally.

I am not a coder—mostly just a front-end designer— and I'm not sure if the problem is w/ Simplenews itself or something else... I suspect it might be an error in my database, not actually in the Simplenews or system.module code, but I have no idea what to look for.

Help...?