Just because the job is unchanged does not mean that
a) The data it is processing is unchanged
b) The software and operating system it is running on is unchanged
c) The hardware is unchanged
d) I could go on
The point is, something has changed which has affected things, and you need to find out what it is.
Start by running the job in a dev environment and seeing whether it fails there, perhaps. Or running on a backup which previously ran fine to see whether it still runs OK (if yes, there's probably a data-related problem.)
If the answer to your question can be found with a brief Google search, please perform the search yourself, rather than expecting one of the SSC members to do it for you.