Why would you need for outlook to be open in order to backup your pst?
If you are thinking of export that is certainly not the way to backup a pst
The method of backing up / saving a data file has been posted here daily

Have you tried Office Diagnostics, from the Office cd, or even scanpst, the
repair tool on your pst?

"Jan Groshan" wrote in message
...
HELP! Suddenly, out of nowhere, my Outlook (2007) will NOT stay open. It
loads, and then I get the "encountered an error and must close" message. I
can't even back up my .pst file because the program won't stay loaded. Any
clues.
(Windows XP SP3)