Follow the link this might help
http://www.red-gate.com/messageboard/viewtopic.php?t=4240
give some more details like.
1. Stand alone server means application and DB are in same server or separate DB server.
2. what is memory utilization at that point.
3. is there any other activity running during the time.
4. what is the DB size which is causing this backup problem and where are you taking backup.