After installing DNN7 >>> I am trying to open it from visual studio .Net but i face this Message:
Message=Object reference not set to an instance of an object.
when execute the follwing line:
if (PortalSettings.ActiveTab.PageHeadText != Null.NullString && !Globals.IsAdminControl())

Please help

Where does this line of code appear?
Which version of DNN? 7.?.?
Which DNN package did you use: source? install?

i am using dnn 7.3.1 install version. this line is already coded in Default Page.aspx

what to do ????

Does the site run correctly as a website, i.e. when you browse to it?

Do you open the solution in the root directory? Then if you run from there you get the stated error?

I just did the following:

1. Open Website and point to the install website.
2. Started debugging

I got exactly the same error that you reported.

That is not the way that I debug DNN sites. This is what I do:

1. Start the website and wait until the home page comes up in the browser
2. In Visual Studio, open the website and point to the install website
3. Debug, Attach to Process

You will need to attach to w3wp.exe.
If there is more than one w3wp.exe, identify the site by the identity user of the app pool.

With all that done, you can set breakpoints and do all of the normal debugging.