Adding Registry entry in HKCU "SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\RunOnce" throws error on SetValue "attempted to perform an unauthorized operation"

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.NET3.5

.NET

C#3.5

I want to add my WPF Application to run automatically on User Login only Once. So, I am using the following code on Application Startup

public void SetStartUpRegistry()
{
     RegistryKey registryKeys = Registry.CurrentUser.OpenSubKey("Software\\Microsoft\\Windows \\CurrentVersion\\RunOnce");
           string[] appKeyNames = registryKeys.GetSubKeyNames();

           var v = from x in appKeyNames
                   where appKeyNames.Contains("KeyName")
                   select x;

           if (v.Count() == 0)
           {
               RegistryKey regkey = Registry.CurrentUser.OpenSubKey("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\RunOnce", true);
               string startPath = Environment.GetFolderPath(Environment.SpecialFolder.Programs)
                  + @"\CompanyName\AppName.appref-ms";
               regkey.SetValue("KeyName", "\"" + startPath + "\"");
           }
       }

This code run perfectly when I run it in VS but when I run it from exe or I deploy it using ClickOnce it throws exception on regkey.SetValue line "attempted to perform an unauthorized operation".

I can even create new subkey in this Registry Key replacing regkey.setValue with regKey.CreateSubKey method. So, I guess it can't be Access Permission issue.

I have complete rights on registry files, I even tried it with administrator account.

What can be the Problem with this code?

I thought Registry.CurrentUser can be accessed by user without any administrative privileges.

The code runs properly if I use Run rather than RunOnce, but I want to use RunOnce.