Hi @vijayarvindr, thanks for posting on the forum and welcome to the SimScale Community 
Usually when this issue happens there is more than one solid body in the domain for a single region analysis type (such as incompressible). Make sure you delete all the solids apart from the Flow region/advanced concepts. Maybe this tutorial is helpful in ilustrating the workflow:
If you’d like to take a closer look at your project, please share the URL (here’s a guide teaching you how: Guide to Clear and Understandable Forum Posting).
Cheers
Igor