That isn't a question we can answer: it's usually a problem with the default constructor of your UserControl.
So remove the instance you dropped on the form, and add an instance programmatically, on a button click:
private void butTestUserControl_Click(object sender, EventArgs e)
{
MyUserControl uc = new MyUserControl();
Controls.Add(uc);
}
Then put a breakpoint on the first line and step into the constructor: follow the code through and look for where the problem is.
Sorry, but we can't do that for you!