Outlook Express database

I am running Outlook Express, and have set it up so that the databases (inbox, outbox et cetera) are available from any point on the network.

I did this by altering the "store root" entry in the registry on every machine and every user to be \\server\outlook\.

It works fine most of the time, but occasionally for reasons utterly beyond
my comprehension it will suddenly change from wanting inbox.dbx to
"inbox (1).dbx" or "inbox (2).dbx" or some number further up the scale.

I do not know where it does this, and would dearly love to find it out so I can stop it doing this!