Hi,
Try following troubleshooting steps.
Try deleting Entourage Preferences and Check.
Follow following steps for the same.
1. Quit Entourage if it is still running.
2. Go to the [OS 10 hard drive]:Users:[Your User
name]:Library

references:Microsoft folder, move the following files to
Desktop.
Carbon Registration Database
Entourage Preferences
Entourage Settings (10)
3. Drag the com.Microsoft.Entourage.plist from the folder "[OS 10 hard
drive]:users:[Your user name]:Library

references" to the desktop.
If problem still exists then you can try rebuilding the Database and check.
Please following the following steps to rebuild the Database.
Step 1 Rebuild Entourage X Database
=====================================
Since the issue can occur if the database in Entourage is not properly
associated,
we can rebuild Entourage X Database to see if the issue can be fixed.
There are two rebuild methods available: a typical and an advanced rebuild.
1) Typical Rebuild
------------------
Hold down OPTION while you launch Entourage. When the message appears that
asks you
what type of rebuild you want to perform, select the Typical Rebuild option,
and
then click Rebuild.
2) Advanced Rebuild
--------------------
If the problem persists after performing a typical rebuild of the database,
we need
to perform an advanced rebuild of the database:
1. Please backup the Entourage X database before Advance Rebuild. The
Entourage
data for each identity is stored in the following folder:
[OS10 Hard drive] \User\ [Current User Name]\ Documents\ Microsoft User
Data\
Office X Identities\ [identity name]
2. Hold down OPTION while you launch Entourage. When the message appears
that asks
you what type of rebuild you want to perform, select the Advanced Rebuild
option,
and then click Rebuild.
Note: When you perform an advanced rebuild, Entourage removes all IMAP,
Hotmail and news messages from the local cache.
For additional information about rebuilding Entourage databases, click the
article
below in Microsoft Knowledge Base:
ENTX: How to Rebuild Your Identity Database in Entourage
http://support.microsoft.com/default.aspx?scid=KB;EN-US;q268322
Note: You have not mentioned which version of Entourage you using. I am
assuming that you are using Entourage X or Entourage 2004. If you are using
Entourage 2001 then you can find the Entourage preferences under... <Hard
disk>/System folder/preferences/Microsoft.
Try removing Entourage preferences from that folder and check.
Hope this resolves the issue.