On alternate days my backup is failing, by the pg_stop_backup process () does not perform or quit.
Version PostgreSQL: 9.1.6
Reporting unusual behavior while running a years-old point release is unlikely to be productive. No one wants to debug something that very well may have been fixed in the meantime.
And, as Robert said, you need to provide considerably more detail than you have if you wish to get help diagnosing your situation. And I too would recommend you not "roll your own" in this area unless you are trying to learn, at a lower-level, how these things work.