I developed RDL using SSRS 2008 and when I deploy the reports on SSRS 2005 running server, It resulted below Error.
"The report definition is not valid. Details: The report definition has an invalid target namespace 'http:/schemas.microsoft.com/sqlserver/reporting/2008/01/reportdefinition' which cannot be upgraded."
Any idea how can I deploy my reports without recreating the reports on SSRS 2005.
There are significant differences between SSRS 2008 and SSRS 2005. I don't think there is any easy way to deploy a 2008 .rdl to 2005.
There were some hacks that would let you deploy a 2005 .rdl to a SSRS 2000 server; but the differences in those formats were minor.
SSRS 2008 started using the tablix control for tables, lists and matrixes. These controls were different types in SSRS 2005.
Sorry for the bad news, but I think you will need to rebuild the report in 2005 or deploy to a 2008 server.