If a job has been entered on the system in error it can be removed by clicking Options > Delete from the job overview screen.
You can only delete a job which has not yet been invoiced since at that stage an invoice has been received from the supplier and the expense has been recharged to the landlord, possibly with an associated maintenance fee.
In order to delete an invoiced job you must first re-open it by changing its status away from invoiced to an open status, e.g. Work Completed. This will remove the charges to the landlord and void the supplier invoice.
Only users with appropriate privileges (determined by their role) will be allowed to delete maintenance jobs, and only those users will see the Delete option; the option is hidden from other users.