Content controls error

Hello
Can I ask, please, what this error refers to?
System.Web.HttpException: Content controls are allowed only in content page that references a master page.
[HttpException (0x80004005): Content controls are allowed only in content page that references a master page.]    System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection) +9651608    System.Web.UI.Page.get_Master() +54    System.Web.UI.Page.ApplyMasterPage() +14    System.Web.UI.Page.PerformPreInit() +45    System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +335
When it refers to a 'content control', does it means something like:
<asp:Label ID="LblDate" runat="server"></asp:Label> What 'mast ...