Program & does not exist

What causes this issue?

A job is to be scheduled with a program which does not exist in your
system.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Check the program name
Using the ABAP editor
In table EWUPGCT or EWUPGSTAT

Error message extract from SAP system. Copyright SAP SE.