When I compile this code, It show me this kind of error type or namespace name profilecommon could not be found. Could someone help me how to solve this?

case "Profile":
ProfileCommon pc = Profile.GetProfile(user.UserName);
foreach (SettingsProperty p in
MultiView1.ActiveViewIndex = 4;


It's telling you that it has no idea what this class is. You are missing a using statement and/or a DLL reference. If you are using Visual Studio, hover the mouse over ProfileCommon and you should get a dropdown box, click it and see if it has the option "add using". If it does, click it. If it doesn't, you are missing the DLL reference.

I don't know how to use DLL reference in my code, if you know please help me?

Go to your project in the explorer and right click, you'll see the menu item 'add reference'. In the window that opens up browse to the DLL you you need and click OK. Once the DLL is referenced add a using statement to your class.