I am working with asp.net reporting using RDLC file. Everything was working fine but now when I add a new dataset, an error occurs.

I have no more info than this, to provide you people to diagnose the problem. Have anyone idea what would be happening?
I just want to add a new dataset.
I solved the problem by following this method:
Add a datasource in your report viewer i.e. in aspx page.
Go to its designer and click on the arrow appearing in front of datasource, and click on it.
Click Refresh Scehma and Save the file.
Go to its code again and comment the datasource code.
Try adding new dataset in rdlc. It will allow adding new datasets now.