AutoCAD Civil 3D 2008 error

Hello,
I just tried to apply Service Pack 1 to AutoCAD Civil 3D 2008 and got this error message which I can’t resolve without having your suggestion. I just visited different forums to find proper answers but could not. Do you have any idea or suggestion to fix this error? Any help would be grateful. Thanks in advance.

Error 1731. The source installation package for the product AutoCAD Civil 3D 2008 is out of sync with the client package. Try the installation again using a valid copy of the installation package ‘C3D.MSI’.
