Registry - writing to HKLM

[Ka-lolek]

Hello,
i have problem cause when i try to write to hkey_local_machine, i get an exception with message

The parameter is incorrect.

the code looks like this:

objReg = Registry.LocalMachine;
RegistryKey obj = objReg.OpenSubKey(Key, true);
                
                if (obj == null) 
                {
                    objReg.CreateSubKey(Key).SetValue(Value, "");
                }
                else
                {
                    objReg.SetValue(Value, "");
                }

i was looking for the solution in the internet, but i only found that the couse can be the lack of administrator privileges..
i added this part:

    [assembly: RegistryPermissionAttribute(SecurityAction.RequestMinimum, ViewAndModify = "HKEY_LOCAL_MACHINE")]

With no result
do you know what cases this problem?
Cheers