You need to check "No authentication required" for MSDTC in Component services.

Do it on SQL Server:

->Admin Tool ->Component service -> expand the service ->right click on my computer -> click...

Thanks for your help.

PS: do I need to change the SA account as well ?

Thanks for your reply.  I just wanted to inform you that all our SQL servers are runs on windows 2003 enterprise but connected to old NT domain.  Network group...