I have installed Visual Studio 2010,it doesn't include crystal Reports, so I downloaded SAP Crystal Report externally from MSDN and installed SAP Crystal Reports.
When I open Visual Studio 2010 I am unable to design existing .RPT files, but when I run an application existing Reports opens.
So what can be the reason why I can't design .rpt files?
You probably need to install Crystal Reports For Visual Studio 2010 on your developer machine as well as Runtime Engine.