See if any of the following apply:
http://support.microsoft.com/default.aspx?scid=kb;en-us;819264
http://support.microsoft.com/default.aspx?scid=kb;EN-US;316541
K. Brian Kelley
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
http://www.netimpress.com/shop/product.asp?ProductID=NI-SQL1
K. Brian Kelley
@kbriankelley