编写如下代码在菜单项中，编译时系统提示错误:

Question

布尔值类型返回的值是“Ture”.
public bool DocumentUndo()
{ 
   bool ifcanUndo=true; //看这里定义或赋值的时候是"true";
   try
   {
  object relval=this.axDHTMLEdit1.QueryStatus(DHTMLEDLib.DHTMLEDITCMDID.DECMD_UNDO);
   if (relval.ToString()=="DECMDF_ENABLED")
   {
   this.axDHTMLEdit1.ExecCommand(DHTMLEDLib.DHTMLEDITCMDID.DECMD_UNDO,DHTMLEDLib.OLECMDEXECOPT.OLECMDEXECOPT_DODEFAULT,ref relval);
   }
   else
  {
　　ifcanUndo=false;
   }
  }
    catch(Exception ex)
    {
MessageBox.Show(ex.Message);
}
return ifcanUndo;
}
-------------------
if (activeChild.DocumentRedo().ToString()=="False")//看这里返回的是"False"或“True”
{ this.tBBRedo.Enabled=false; this.tBBundo.Enabled=true;
}