TabPage does not support Visible or Enabled: they are inherited, masked so you can't access them from Intellisense, and deliberately disabled.
You can access them programmatically by typing the names:
tabPage1.Visible = false;
tabPage2.Enabled = false;
And your code will compile.
But they will have no effect.
You cannot disable or hide a tabpage - you can only remove it from the TabPages collection of the parent TabControl, or add a Panel which fills the tab page and use the Enabled property of that.