Exchange 2003 - Recipient Update Service - Changing the DC

Hello Everyone,
About 3 monts ago I demoted and removed a DC from our domain. After doing this we did not notice any issues with our exchange 2003 server or email.   Just the other day, I was looking in the application log on the exchange server saw the following error:  

Event Type:      Error
Event Source:      MSExchangeAL
Event Category:      LDAP Operations
Event ID:      8026
Date:            2/25/2011
Time:            6:16:23 AM
User:            N/A
Computer:      EXCHANGE SERVER
Description:
LDAP Bind was unsuccessful on directory “removed dc name” for distinguished name

I did some research and found out the RUS is still pointing to this removed server.  I see how to change it to the new DC, but I want to know if I make this change how will it affect my users since it has been about 3 months and should I do this change after hours?

Thanks,

Bill