Hi Abhilash
Sorry I couldn't make my self clear.
My question was I have created a report using CR 2008 and xml and web services as my data connection.
Now I want to use same report with CR 2008 SP5, and try to preview report it gives "Unknown data Connection Error".
When I try to browse the data from set Data source location from field explorer it gives no item found and because of that only I was getting "Unknown data Connection Error".
So i tried to create new connection for the same report and update the existing one with newly created Data connection and then I was able to view the preview 
.
But as I close and reopen it my new connnection lost and I have only those data connection which I created using CR 2008.
Errors are attached you can have a look
Have you got the problem?
-Rahul