Note - Ghost Schedulable Classes Blocking Deployment and https://success.salesforce.com/issues_view?id=a1p30000000STwPAAW may be related, but I'm not sure
Someone in our org made the poor decision to create a class called "Account," which caused errors across a few classes which used the Account standard object. Initially, I tried deleting the class, but got the error:
"This Schedulable class is in use."
The code was simply this:
public class Account {
}
In order to solve the initial issue, I changed the class name to "Accountd", which resolved the name errors, but still cannot delete the class.