we're seeing this error in cron on one of our sites causing cron to completely fail:

!!! Coding error detected, it must be fixed by a programmer: User ID does not exist or is deleted! !!!
!! userid:2043
Error code: codingerror !!
!! Stack trace: * line 1623 of /lib/accesslib.php: coding_exception thrown

• line 1311 of /lib/enrollib.php: call to role_assign()
• line 243 of /enrol/flatfile/lib.php: call to enrol_plugin->enrol_user()
• line 144 of /enrol/flatfile/lib.php: call to enrol_flatfile_plugin->process_records()
• line 54 of /enrol/flatfile/lib.php: call to enrol_flatfile_plugin->process_file()
• line 243 of /lib/cronlib.php: call to enrol_flatfile_plugin->cron()
• line 88 of /admin/cron.php: call to cron_run()

flatfile shouldn't try to handle users that have been deleted.