"You do not have permission to edit Service Dispatch"
In order to edit Service Dispatch you must have the "Can edit Service Dispatches" checkbox checked in your User Admin page.
If you try to edit a Service Dispatch and receive this pop up you need to request access through your Admin:
If you are an Administrator you can access the user account and grant the edit ability by going to Toolbox > Admin > User Administration and enable the following permission titled "Can Edit Service Dispatches"
If you cannot edit Service Dispatch Invoices you will need to activate this permission: