Accessing sharepoint from Powershell-script from c# application

Hello I'm trying to access a sharepoint list from powershell. The powershell script is executed from a c# application.

If I run the from c# application I get the following exception:

Exception calling ".ctor" with "1" argument(s): "The Web application at http://pc/websites/Test4/ could not be found. Verify that you have typed the URL correctly. If the URL should be serving existing content, the system administrator may need to add a new request URL mapping to the intended application."

My Code:

C#

     string cmdArg = "C:\\Scripts\\GroupChangeGroup.ps1 1";
                    Runspace runspace = RunspaceFactory.CreateRunspace();
                    runspace.ApartmentState = System.Threading.ApartmentState.STA;
                    runspace.ThreadOptions = PSThreadOptions.UseCurrentThread;
                        runspace.Open();
                    Pipeline pipeline = runspace.CreatePipeline();

 Command newcom = new Command("Add-PSSnapin");
                      newcom.Parameters.Add("Name", "microsoft.exchange.management.powershell.e2010");
                      pipeline.Commands.Add(newcom);

                  Command newcom2 = new Command("Add-PSSnapin");
                  newcom2.Parameters.Add("Name", "Microsoft.SharePOint.POwershell");
                  pipeline.Commands.Add(newcom2);

                    pipeline.Commands.AddScript(cmdArg);
                    pipeline.Commands[0].MergeMyResults(PipelineResultTypes.Error, PipelineResultTypes.Output);
                    Collection<PSObject> results = pipeline.Invoke();
                    var error = pipeline.Error.ReadToEnd();
                    runspace.Close();

Powershell

$site = New-Object Microsoft.SharePoint.SPSite("http://pc/websites/Test4/")
$web = $site.OpenWeb()
$list = $web.Lists["GroupsList - ListInstance1"]
$listitem = $list.Items.GetItemByID(3)

If I execute the application from PS there is no problem. (same user context)

The User is Member of WSS_ADMIN_WPG