Current thread must be set to single thread apartment (STA) mode before OLE calls can be made. Ensure that your Main function has STAThreadAttribute marked on it.

var thread = new Thread(() => { //MessageBox.Show(pressedKey);
if(pressedKey.Equals("Space")||pressedKey.Equals("Tab"))
{
System.Windows.Forms.Clipboard.SetText(pressedKey);
IDataObject key = Clipboard.GetDataObject();
string mykey = key.GetData(DataFormats.Text).ToString();
MessageBox.Show(mykey);
}
});
new Thread.ApartmentState = ApartmentState.STA;
new Thread.Start();

Gives me error:
Error 1 A new expression requires (), [], or {} after type (this is for the line :newThread.ApartmentState = ApartmentState.STA;)

Error 2 'System.Threading.Thread.ApartmentState' is a 'property' but is used like a 'type'
Error 3 'System.Threading.Thread.Start(object)' is a 'method' but is used like a 'type'

I'm using a thread because it takes too much time for the messagebox to show up.. response time is faster with a thread..

Thanks a lot for the link bill :) I fixed it.. :)