Outlook IMAP Problems

I have a user using Outlook 2003 with all of the latest updates, and her mail database on the notes server is about 1.4gb. When she tries to access her email, she gets this error: “Can’t open this item. the operation could not be completed because the connection is busy performing other tasks. Please try again later”. Is this because her mail database is so big? If that’s the case, shouldn’t it be cached on her local drive?

Thanks