Atlast I found the solution 
all you need to do is copy a set of JS files into your website's contents folder.
Here are the steps to fix this issue:
go to "C:\Inetpub\wwwroot" or where ever your "wwwroot" folder is.
copy the folder called "aspnet_client" from there and paste it into your website's content folder.
thats it!
Here I have assumed that you have already installed the right version of crystal redistributeables on your webserver.
to check if it is done properly see if there is a folder called "CrystalReportWebFormViewer3" and further subfolder in it containing html, js, css and images at this location:
"C:\inetpub\wwwroot\aspnet_client\system_web\2_0_50727\CrystalReportWebFormViewer3"
hope it will solve the issue.